fix test token scoping: override GITHUB_TOKEN via OIDC in ensureGitHubToken

the runner's GITHUB_TOKEN (scoped to pullfrog/app) was leaking into
test subprocesses targeting pullfrog/test-repo, causing 400s from the
Pullfrog API on run-context fetches.

instead of deleting GITHUB_TOKEN from the subprocess env,
ensureGitHubToken now always mints a fresh OIDC token scoped to
GITHUB_REPOSITORY when OIDC is available — replacing any inherited
token with a correctly-scoped one.

also adds an informative throw in acquireTokenViaGitHubApp when
GITHUB_APP_ID/GITHUB_PRIVATE_KEY are missing.

Made-with: Cursor

get-installation-token/entry

@@ -25898,10 +25898,15 @@ var findInstallationId = async (jwt, repoOwner, repoName) => {
   );
 };
 async function acquireTokenViaGitHubApp(opts) {
+  if (!process.env.GITHUB_APP_ID || !process.env.GITHUB_PRIVATE_KEY) {
+    throw new Error(
+      "cannot acquire token via GitHub App: GITHUB_APP_ID and GITHUB_PRIVATE_KEY must be set"
+    );
+  }
   const repoContext = parseRepoContext();
   const config = {
     appId: process.env.GITHUB_APP_ID,
-    privateKey: process.env.GITHUB_PRIVATE_KEY?.replace(/\\n/g, "\n"),
+    privateKey: process.env.GITHUB_PRIVATE_KEY.replace(/\\n/g, "\n"),
     repoOwner: repoContext.owner,
     repoName: repoContext.name
   };