feat: explain refusals to delete or rerun an unfinished run

Gitea refuses to delete or rerun a run that has not finished with "this
workflow run is not done". Report "run 37 has not finished; cancel it first:
tea run cancel 37", and cover the next steps added to refusals in tests.

Signed-off-by: bircni <bircni@icloud.com>

internal/services/errors_test.go

@@ -52,6 +52,7 @@ func TestClassifyRequestNamesTheResource(t *testing.T) {
 		{"repository exists", "POST", "/api/v1/user/repos", "The repository with the same name already exists.", 409, "repository already exists"},
 		{"org repository exists", "POST", "/api/v1/orgs/acme/repos", "The repository with the same name already exists.", 409, "repository already exists"},
 		{"run completed", "POST", "/api/v1/repos/alice/x/actions/runs/35/cancel", "run is already completed", 409, "run 35 is already completed"},
+		{"run not done", "DELETE", "/api/v1/repos/alice/x/actions/runs/37", "this workflow run is not done", 400, "run 37 has not finished"},
 		{"workflow disabled", "POST", "/api/v1/repos/alice/x/actions/workflows/nightly.yaml/dispatches", "workflow is disabled", 403, "workflow nightly.yaml is disabled"},
 		{"key in use", "POST", "/api/v1/user/keys", "Key content has been used as non-deploy key", 422, "this SSH key is already registered"},
 		{"unknown assignee", "POST", "/api/v1/repos/alice/x/issues", "Assignee does not exist: [name: user does not exist [uid: 0, name: nobody123]]", 422, `user "nobody123" not found`},