Add GIT_BRANCH_MISMATCH_UPSTREAM_IGNORELIST allowing to ignore new upstream release

Packages versions coming from Debian are correctly parsed, so we don't have to
whitelist them, however in Apertis we use the ~v202X suffix which is to
misinterpreted by dashboard and lead to confusion when comparing versions.
For example, the dashboard the of downstream complains about:

Version in apertis/v2023/5.2.5~ds0-1+apertis0 is higher than version 5.2.5~ds0-1+apertis0~v2023 in upstream apertis/v2023

Which is true, but due to our workflow, the version apertis/v2023/5.2.5~ds0-1+apertis0
should not land in v2023 this is the reason of why we add the problematic
suffix allowing us to backport targeted changes to a previous release.
Adding the logic in the dashboard to correctly interpret the ~v202X is
not trivial, so for now we can teach it to ignore some versions.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>