GitHub: re-enable the linter

The linter was disabled before due to a bug. Since the bug was likely
caused by an issue with a go module in a dependency project which was
updated in the meantime, we attempt to re-enable the linter in the CI
now.

Author: guggero

.github/workflows/main.yml

@@ -156,9 +156,6 @@ jobs:
   # lint code
   ########################
   lint:
-    # Temporarily disabling the linter while this issue persists:
-    #       https://github.com/golangci/golangci-lint/discussions/1920
-    if: false
     name: lint
     runs-on: ubuntu-latest
     steps: