fix(trufflehog): ignore missing checkout extraheader

checkout v7 no longer sets http.https://github.com/.extraheader, so
unset-all exits 5 and aborts the scan. Treat a missing key as success.

Author: isaiah-grafana

.github/workflows/reusable-trufflehog.yml

@@ -63,7 +63,7 @@ jobs:
         run: git fetch --depth=1 origin "${MERGE_GROUP_BASE_SHA}" "${MERGE_GROUP_HEAD_SHA}"
 
       - name: Remove persisted credentials
-        run: git config --unset-all http.https://github.com/.extraheader
+        run: git config --unset-all http.https://github.com/.extraheader || true
 
       - name: Fetch org-wide TruffleHog exclude patterns
         env: