[macos-runner] Force login keychain into the job session's search list

Unlocking alone wasn't enough - the launchd session's default keychain
search list apparently doesn't include the login keychain by default,
so sigh/fastlane still found zero identities even after a successful
unlock. Explicitly set it as both the search list and default keychain,
and print find-identity in the step itself to verify before fastlane runs.

.gitea/workflows/release.yml

@@ -55,7 +55,11 @@ jobs:
           EOF
 
       - name: Unlock keychain
-        run: security unlock-keychain -p "${{ secrets.MAC_KEYCHAIN_PASSWORD }}" ~/Library/Keychains/login.keychain-db
+        run: |
+          security unlock-keychain -p "${{ secrets.MAC_KEYCHAIN_PASSWORD }}" ~/Library/Keychains/login.keychain-db
+          security list-keychains -d user -s ~/Library/Keychains/login.keychain-db
+          security default-keychain -d user -s ~/Library/Keychains/login.keychain-db
+          security find-identity -v -p codesigning
 
       - name: fastlane release
         run: |