๐Ÿ› fix --exit-code in scanner.py

There's a code path in scanner.py where scanner --exit-code can find problems but will not terminate with an error code. So here's a fix for that.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f