fix(exec): serve the v4 artifact API so upload-artifact v4 and later work (#1341)

`exec` forwarded the toolkit's ArtifactService calls to an instance it never registered, and its random runtime token held no backend IDs, so `actions/upload-artifact` and `actions/download-artifact` v4 and later failed.

The local artifact server now serves the v4 API, including the single Put Blob uploads docker/build-push-action uses. `exec` gives each workflow its own unsigned JWT runtime token and artifact run, so artifact names conflict and carry over between runs as on GitHub. Artifacts default to a temporary directory instead of the workspace that jobs copy.

Co-authored-by: silverwind <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1341
Reviewed-by: Lunny Xiao <[email protected]>
Reviewed-by: silverwind <[email protected]>
Co-authored-by: bircni <[email protected]>

e2e/compatibility_test.go

@@ -30,6 +30,7 @@ func TestCompatibility(t *testing.T) {
 	t.Run("cancellation_and_log_streaming", testRunCancellation)
 	t.Run("dispatch", testWorkflowDispatch)
 	t.Run("builtin_checkout", testBuiltinCheckout)
+	t.Run("exec_artifacts", testExecArtifacts)
 	t.Run("moving_action_ref", testMovingActionRef)
 	t.Run("ephemeral", testEphemeralRunner)
 	t.Run("failure_paths", testFailurePaths)