Merge branch 'ps/doc-packfile-vs-pack-file' into maint

Doc consistency updates.

* ps/doc-packfile-vs-pack-file:
doc: fix inconsistent spelling of "packfile"
pack-protocol.txt: fix insconsistent spelling of "packfile"
git-unpack-objects.txt: fix inconsistent spelling of "packfile"
git-verify-pack.txt: fix inconsistent spelling of "packfile"