feat(actions): add force-cancel workflow run API (#38756)

Add `POST /repos/{owner}/{repo}/actions/runs/{run}/force-cancel`, the
counterpart of [GitHub's force-cancel endpoint](https://docs.github.com/en/rest/actions/workflow-runs?apiVersion=2026-03-10#force-cancel-a-workflow-run).

It cancels a run like `POST .../cancel`, but bypasses the graceful
cancelling handshake with the runner and stops running tasks
immediately.

Permissions and responses match the `/cancel` endpoint.

References:

- https://github.blog/changelog/2023-09-21-github-actions-force-cancel-workflows/
- https://docs.github.com/en/rest/actions/workflow-runs?apiVersion=2026-03-10#force-cancel-a-workflow-run
- https://github.com/orgs/community/discussions/123240

templates/swagger/v1-openapi3.generated.json

@@ -16802,6 +16802,62 @@
         ]
       }
     },
+    "/repos/{owner}/{repo}/actions/runs/{run}/force-cancel": {
+      "post": {
+        "description": "Cancels a workflow run without waiting for its runners to acknowledge the cancellation.\nThe jobs are marked cancelled at once and anything a runner reports for them afterwards is discarded.\nOnly use this endpoint when the workflow run does not respond to `POST /repos/{owner}/{repo}/actions/runs/{run}/cancel`.\n",
+        "operationId": "forceCancelWorkflowRun",
+        "parameters": [
+          {
+            "description": "owner of the repo",
+            "in": "path",
+            "name": "owner",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          },
+          {
+            "description": "name of the repository",
+            "in": "path",
+            "name": "repo",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          },
+          {
+            "description": "run ID",
+            "in": "path",
+            "name": "run",
+            "required": true,
+            "schema": {
+              "type": "integer"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "$ref": "#/components/responses/WorkflowRun"
+          },
+          "400": {
+            "$ref": "#/components/responses/error"
+          },
+          "403": {
+            "$ref": "#/components/responses/forbidden"
+          },
+          "404": {
+            "$ref": "#/components/responses/notFound"
+          },
+          "409": {
+            "$ref": "#/components/responses/conflict"
+          }
+        },
+        "summary": "Force-cancel a workflow run",
+        "tags": [
+          "repository"
+        ]
+      }
+    },
     "/repos/{owner}/{repo}/actions/runs/{run}/jobs": {
       "get": {
         "operationId": "listWorkflowRunJobs",

templates/swagger/v1-swagger.generated.json

@@ -5737,6 +5737,59 @@
         }
       }
     },
+    "/repos/{owner}/{repo}/actions/runs/{run}/force-cancel": {
+      "post": {
+        "description": "Cancels a workflow run without waiting for its runners to acknowledge the cancellation.\nThe jobs are marked cancelled at once and anything a runner reports for them afterwards is discarded.\nOnly use this endpoint when the workflow run does not respond to `POST /repos/{owner}/{repo}/actions/runs/{run}/cancel`.\n",
+        "produces": [
+          "application/json"
+        ],
+        "tags": [
+          "repository"
+        ],
+        "summary": "Force-cancel a workflow run",
+        "operationId": "forceCancelWorkflowRun",
+        "parameters": [
+          {
+            "type": "string",
+            "description": "owner of the repo",
+            "name": "owner",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "name of the repository",
+            "name": "repo",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "integer",
+            "description": "run ID",
+            "name": "run",
+            "in": "path",
+            "required": true
+          }
+        ],
+        "responses": {
+          "200": {
+            "$ref": "#/responses/WorkflowRun"
+          },
+          "400": {
+            "$ref": "#/responses/error"
+          },
+          "403": {
+            "$ref": "#/responses/forbidden"
+          },
+          "404": {
+            "$ref": "#/responses/notFound"
+          },
+          "409": {
+            "$ref": "#/responses/conflict"
+          }
+        }
+      }
+    },
     "/repos/{owner}/{repo}/actions/runs/{run}/jobs": {
       "get": {
         "produces": [