Restore git global config

`setup-git-redirect.sh` is needed for tests, because go needs SSH
authentication, when downloading modules dependencies. The redirect
script, though, does not revert the global changes done to the git
config (in that case: SSH instead of HTTPS). The `checkout` action,
on the other hand, needs the HTTPS for checkout, because the SSH key at the
beginning of the action is no longer available, it was properly cleaned
up in the `webfactory/ssh-agent` post clean up.

Implementing workaround as in webfactory/ssh-agent#184

.github/workflows/test.yml

@@ -44,3 +44,8 @@ jobs:
           ssh-private-key: ${{ secrets.BOT_PRIVATE_KEY }}
       - run: ./hack/setup-git-redirect.sh
       - run: make test
+      - name: Restore git global config
+        if: always()
+        run: |
+          MATCH=$(grep -o 'git@.*github\.com:' ~/.gitconfig)
+          git config --global --remove-section url.${MATCH}