meson: fix protoc/protobuf compatility check

libprotobuf a.b.c.d and a.b are compatible with any a.b protoc version. But only those.

For example the 3.21.1.0 libprotobuf is compatible with my Debian 3.21.12 protoc.

This is how it's validated in configure.ac: https://code.videolan.org/videolan/vlc/-/blob/0085375629d4d424a86a144d347e0febbfc9cbea/configure.ac?page=4#L3939