fix(terraform): fix broken --skip-path command line option

[brendanator]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Description

Fixes #7290 where the excluded_paths regex was always garbled, regardless of which patterns were passed via --skip-path

Here's what the code before and after does:

>>> excluded_paths = ['testdata', 'fixtures']

>>> '|'.join(f"({excluded_paths})")             # before
"(|[|'|t|e|s|t|d|a|t|a|'|,| |'|f|i|x|t|u|r|e|s|'|]|)"

>>> '|'.join(f"({p})" for p in excluded_paths)  # after
'(testdata)|(fixtures)'

The fix iterates excluded_paths so each pattern becomes its own group, which is what the surrounding code already expects.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my feature, policy, or fix is effective and works
• New and existing tests pass locally with my changes