feat(actions): support $/ prefix in reusable workflow uses: (#38822)

Fixes: https://github.com/go-gitea/gitea/issues/38818

Accepts GitHub's `$/` self-repository prefix in a reusable workflow
`uses:`, alongside `./`.

Gitea's `./` already resolves against the caller's own source repo and
commit, which is what `$/` means, so the two are aliases here. Cycle
detection folds both prefixes onto one key.

Related PR for step-level support:
https://gitea.com/gitea/runner/pulls/1150

modules/actions/jobparser/uses_test.go

@@ -53,6 +53,11 @@ func TestParseUses(t *testing.T) {
 				in:   "./.gitea/custom_workflows/x.yaml",
 				want: UsesRef{Kind: UsesKindLocalSameRepo, Path: ".gitea/custom_workflows/x.yaml"},
 			},
+			{
+				name: "self-repo prefix",
+				in:   "$/.gitea/workflows/build.yml",
+				want: UsesRef{Kind: UsesKindLocalSameRepo, Path: ".gitea/workflows/build.yml"},
+			},
 			{
 				name: "leading/trailing whitespace is trimmed",
 				in:   "  ./.gitea/workflows/build.yml  ",
@@ -160,6 +165,7 @@ func TestParseUses(t *testing.T) {
 
 			// Same-repo malformed (note: a wrong *directory* parses and should be rejected by the caller)
 			{name: "same-repo with @ref", in: "./.gitea/workflows/build.yml@v1"},
+			{name: "self-repo with @ref", in: "$/.gitea/workflows/build.yml@v1"},
 			{name: "same-repo wrong extension", in: "./.gitea/workflows/build.txt"},
 			{name: "same-repo missing extension", in: "./.gitea/workflows/build"},
 			{name: "same-repo absolute path", in: "/.gitea/workflows/build.yml"},