fix(api): document X-Total-Count instead of non-existent X-Total header (#38717)

The `CommitList` and `ChangedFileList` swagger responses documented an
`X-Total` response header that their endpoints never send, they send
`X-Total-Count` via `SetTotalCountHeader`. This renames the documented
header and regenerates the spec.

`repoGetAllCommits` also uses `CommitList` and sends both headers, so
the new name is accurate for all three endpoints.

Also corrects `ChangedFileList` describing its headers as commit counts.

Documentation only, no handler behaviour changes.

Fixes https://github.com/go-gitea/gitea/issues/22048

---------

Signed-off-by: davidpavlovschi <davidpavlov2048@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

templates/swagger/v1-openapi3.generated.json

@@ -213,14 +213,14 @@
             }
           },
           "X-PerPage": {
-            "description": "Commits per page",
+            "description": "Files per page",
             "schema": {
               "format": "int64",
               "type": "integer"
             }
           },
-          "X-Total": {
-            "description": "Total commit count",
+          "X-Total-Count": {
+            "description": "Total file count",
             "schema": {
               "format": "int64",
               "type": "integer"
@@ -311,7 +311,7 @@
               "type": "integer"
             }
           },
-          "X-Total": {
+          "X-Total-Count": {
             "description": "Total commit count",
             "schema": {
               "format": "int64",