src: use git safe.directory to get the revision number

In the release build runner this seems to be an issue ¹.

Making all in src
Makefile:3751: warning: ignoring prerequisites on suffix rule definition
Makefile:3755: warning: ignoring prerequisites on suffix rule definition
make[2]: Entering directory '/builds/videolan/vlc/winarm64-ucrt/src'
  CC       fourcc_gen
  GEN      stamp-revision
  GEN      ../include/vlc_about.h
fatal: detected dubious ownership in repository at '/builds/videolan/vlc'
To add an exception for this directory, call:
	git config --global --add safe.directory /builds/videolan/vlc
cat: /builds/videolan/vlc/extras/package/win32/../../../src/revision.txt: No such file or directory
make[2]: *** [Makefile:3781: stamp-revision] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: Leaving directory '/builds/videolan/vlc/winarm64-ucrt/src'
make[1]: *** [Makefile:1573: all-recursive] Error 1
make[1]: Leaving directory '/builds/videolan/vlc/winarm64-ucrt'
make: *** [Makefile:1460: all] Error 2

1. https://code.videolan.org/videolan/vlc/-/jobs/2288139 ↩