Existing repositories are no longer updated if Git tag is changed

[mliebischer]

I am coming from v2 and have recently started with v4. I have noticed that updating the Git tag within the branch option no longer update existing repositories correctly.

Steps to reproduce:

1. Create a simple configuration file with the branch option set to an existing Git tag, e.g. 8.0.0 for plone.restapi.

[plone.restapi]
url = https://github.com/plone/plone.restapi.git
branch = 8.0.0

3. Run mxdev -c mxdev.ini to fetch the package initially.
4. Change the branch option to 9.0.0.

[plone.restapi]
url = https://github.com/plone/plone.restapi.git
branch = 9.0.0

6. Run mxdev -c mxdev.ini again to update your existing repo.
7. Check the Git tag of the currently checked out repository. You can use git describe --tags for this.

Actual result:
You will see that the repository remains on the old tag 8.0.0.

Expected result:
The repository should be updated to 9.0.0.

Affected versions:

pip install mxdev==4.0.3 # broken
pip install mxdev==2.1.0 # works

I suspect this is related to the recent VCS code change, but I have not checked this further, see https://github.com/mxstack/mxdev/blob/main/CHANGES.md#300b1-2022-11-21

Side note:
Changing branch = main to branch = portlets works fine. It seems that only tag does not work anymore.