scripts/documentation-file-ref-check: don't check perl/python scripts

scripts/documentation-file-ref-check: don't check perl/python scripts

Such scripts may have regular expressions, which would make the
parser confusing. Also, they shouldn't hardcode filenames there,
so skipping them is OK.

While here, also don't check references on extensions used for file
backup and patch rej/orig.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/712bfc8412ee5ad8ab43dd21a8c30fc858eff5a6.1739182025.git.mchehab+huawei@kernel.org