Added support for export LC_ALL=C.UTF-8 to the shell linter
This allows us to explicitly set the codeset to UTF-8.
arc lint on the following cases:
- script with export LC_ALL=C
- script with no LC_ALL set. Fails as expected.
- script with export LC_ALL=C.UTF-8
- script with export LC_ALL=C.UTF-9 Fails as expected (sanity check that we don't accidentally match on export LC_ALL=C)
Reviewers: #bitcoin_abc, deadalnix, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D4183