melange bump: don't skip main git checkout when mangled package versio…

[rawlingsj]

…n is used

There are cases where we use a mangled package version var when doing a git checkout of the main source repo. Let's update the git commit in these cases. The check was originally added in #975 but only identified the main repo using ${{package.version}}, we should include ${{vars.mangled-package-version}}.

The reason is so the update bot doesn't bump all commits if there are multiple git checkout steps, as they are likely not the ones that the update: block is configured for.

There may be a better way to identify the main git checkout, not sure of one now though.

[rawlingsj]

fyi @xnox

[xnox]

Scope of change:

$ echo $(git grep 'tag:.*vars.mangled-package-version' | wc -l)
29