It should detect multi-line secrets

[pburkholder]

Back with gitleaks 7.x we had this test:

@test "it fails a flask secret key" {
  cat > $REPO_PATH/webapp.py <<END
    app.secret_key = (
        '39a45464-cb1d-4b8d-aa1f-83c7c04fa673'
    )
END
    run testCommit $REPO_PATH
    should_fail
}

But that stopped working in 8.8.4.

For now I've changed the test to single line, but it would be good to detect across the newline.

I don't know if this is a bug/feature in 8.8.4 or perhaps in Go regexes.

Security considerations

1. This issue is safe, 2. Fixing this is a good thing

[markdboyd]

This might be fixed by 16a52d8. Let me know what you think.