Support fetching without the --progress option

Setting the `progress` option to false in the `with` section of the
workflow step will cause git fetch to run without `--progress`.

The motivation is to be able to suppress the noisy progress status
output which adds many hundreds of "remote: Counting objects: 85%
(386/453)" and similar lines in the workflow log.

This should be sufficient to resolve #894 and its older friends,
though the solution is different to the one proposed there because
it doesn't use the --quiet flag. IIUC git doesn't show the progress
status by default since the output is not a terminal, so that's why
removing the --progress option is all that's needed.

Adding the --quiet flag doesn't make a lot of difference once the
--progress flag is removed, and actually I think using --quiet would
suppress some other more useful output that would be better left
visible.

Signed-off-by: Simon Baird <sbaird@redhat.com>

action.yml

@@ -68,6 +68,9 @@ inputs:
   fetch-tags:
     description: 'Whether to fetch tags, even if fetch-depth > 0.'
     default: false
+  show-progress:
+    description: 'Whether to show progress status output when fetching.'
+    default: true
   lfs:
     description: 'Whether to download Git-LFS files'
     default: false