build: bump to version 13.0.3 for the point release

Second attempt for a new point release. Apparently the release script pushes the tag using to the default, main branch as opposed to the correct one (13 in this case). This seems to happen when it doesn't find a proper @upstream configure branch. I don't have a branch entry set for 13.0. Creating one by checking out a local 13.0 branch fixes that.

Unfortunately the check in the release script is not enough to accommodate for this, and it allows to push tags based on default, main branch, which happened again. Meanwhile, just do another meson.build bump instead of destroying/creating one similarly to what I did last time when this happened.