ewaol-config/qa-checks: Include additional default file type for shell check

Depending on the version of the host's libmagic library, python-magic can
report different file-type strings. This patch adds "bash script" as an
included file type for systems running earlier versions of the library, before
bash files evaluate as "bourne-again shell script".

Issue-Id: SCM-3910
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: I4f2b296995d04af4d1899807c48452263aa18d91