[scarthgap][backport] Fix packaging of stale externalsrc recipes

[Marcus Comstedt <marcus.comstedt@requtech.se>]

Hi.

After upgrading from dunfell to scarthgap (due to the EOL of the
former), I discovered that bitbake would occasionally package versions
of externalsrc packages that did not contain the latest changes.

The details are in this bug:

https://bugzilla.yoctoproject.org/show_bug.cgi?id=15646

As Ross Burton noted, this issue has already been identified and fixed
on master, in commit

475759fdab7200488b2a568b2ba1aa31a456d113

I have verified that this commit can be cleanly cherry-picked to
scarthgap and does indeed fix the issue.

Since this is a rather serious issue (at least to me, and probably
anyone else using the same externalsrc recipe in more than one yocto
build), I would like to see this commit backported to the scarthgap
branch.  The only alternative for me would be to fork openembedded-core
in order to do the cherry-pick myself.

I believe the same issue applies to kirkstone, although I have no
personal stake in it getting backported to that branch.  And the same
for non-LTS branch styhead.  All other affected branches are EOL, AFAICT.

Thanks


  // Marcus