[FIX] checkers: Don't faill when variables.sh contains comments

Currently, all lines of the `variables.sh` file should follow the
pattern:
EXPORT varname=value

However, that pattern disallows lines that are just comments, e.g.
starting with `#`.

This commits allows also comments as valid lines.
1 job for master-variables_line_comment-luisg in 10 seconds (queued for 2 minutes and 10 seconds)
latest
Status Job ID Name Coverage
  Test
passed #665832
lint
test_install

00:00:10