nginx: actually download the specified git commit hash

nginx: actually download the specified git commit hash

Currently, we are using Download recipes to download the various modules,
however we are using then with PROTO:=git but SOURCE_VERSION is not set,
only VERSION variable so thus the dl_github_archive.py scripts gets called
with --version="" instead of being actually passed the desired commit hash
and thus actually the git head is fetched.

This explains why currently buildbots are failling with
nginx-mod-njs/104-endianness_fix.patch failling to apply since buildbots
are using prepackaged tarballs which are different than what we get when
manually building.

So, lets set SOURCE_VERSION to make sure we actually fetch the desired
git commit hash.

Signed-off-by: Robert Marko <redacted>