patch 9.2.0523: tests: no test for using shellescape() in combination with :!

patch 9.2.0523: tests: no test for using shellescape() in combination with :!

Problem:  tests: no test for using shellescape() in combination with :!
Solution: Add a test that checks runtime files for using wrong
          combination of shellescape() with ! ex command

This has lead to a few security relevant issues, so add a test that
checks all runtime files for any ! followed by a shellescape() that does
not use the {special} arg.

related: Commit: 3fb5e58fbc63d86a3e65f1a141b0d67af2 (patch 9.2.0479:
         [security]: runtime(tar): command injection in tar plugin)

closes: #20286

Supported by AI

Signed-off-by: Christian Brabandt <cb@256bit.org>