Fix Mac tests by making an unshallow copy of Homebrew repos
Fix Mac tests by making an unshallow copy of Homebrew repos

It seems that updating shallow Git clones is expensive, and as a result
Homebrew recently started refusing to update shallow clones (see
https://github.com/Homebrew/discussions/discussions/226). This commit
tries to fix the problem by making these repos into full clones before
running "brew update".

I also came across another error about there being a conflicting version
of pip3 in /usr/local. I suspect that is related to the other Python
binaries that the script has to delete, so I added pip3 to the list and
that seemed to solve the problem.

google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf