tests/test-hooklib-reject_merge_commits.t

setup: exclude the git extension from py2 builds

This can't be built on Windows with the py2 compiler, and while old versions can
be installed via pip on Linux, I can't get the tests to run (even with py3.8)
using pygit2 0.28.2.  Some manually run commands work, and others spew stack
traces that don't occur with the current 1.4.0 release using py3.

Differential Revision: https://phab.mercurial-scm.org/D9604

  $ cat <<EOF >> $HGRCPATH
  > [extensions]
  > hooklib =
  > 
  > [phases]
  > publish = False
  > EOF
  $ hg init a
  $ hg --cwd a debugbuilddag '.:parent.:childa*parent/childa<parent@otherbranch./childa'
  $ hg --cwd a log -G
  o    changeset:   4:a9fb040caedd
  |\   branch:      otherbranch
  | |  tag:         tip
  | |  parent:      3:af739dfc49b4
  | |  parent:      1:66f7d451a68b
  | |  user:        debugbuilddag
  | |  date:        Thu Jan 01 00:00:04 1970 +0000
  | |  summary:     r4
  | |
  | o  changeset:   3:af739dfc49b4
  | |  branch:      otherbranch
  | |  parent:      0:1ea73414a91b
  | |  user:        debugbuilddag
  | |  date:        Thu Jan 01 00:00:03 1970 +0000
  | |  summary:     r3
  | |
  +---o  changeset:   2:a6b287721c3b
  | |/   parent:      0:1ea73414a91b
  | |    parent:      1:66f7d451a68b
  | |    user:        debugbuilddag
  | |    date:        Thu Jan 01 00:00:02 1970 +0000
  | |    summary:     r2
  | |
  o |  changeset:   1:66f7d451a68b
  |/   tag:         childa
  |    user:        debugbuilddag
  |    date:        Thu Jan 01 00:00:01 1970 +0000
  |    summary:     r1
  |
  o  changeset:   0:1ea73414a91b
     tag:         parent
     user:        debugbuilddag
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     r0
  
  $ hg init b
  $ cat <<EOF >> b/.hg/hgrc
  > [hooks]
  > pretxnchangegroup.reject_merge_commits = \
  >   python:hgext.hooklib.reject_merge_commits.hook
  > EOF
  $ hg --cwd b pull ../a -r a6b287721c3b
  pulling from ../a
  adding changesets
  adding manifests
  adding file changes
  error: pretxnchangegroup.reject_merge_commits hook failed: a6b287721c3b rejected as merge on the same branch. Please consider rebase.
  transaction abort!
  rollback completed
  abort: a6b287721c3b rejected as merge on the same branch. Please consider rebase.
  [255]
  $ hg --cwd b pull ../a -r 1ea73414a91b
  pulling from ../a
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files
  new changesets 1ea73414a91b (1 drafts)
  (run 'hg update' to get a working copy)
  $ hg --cwd b pull ../a -r a9fb040caedd
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 0 changes to 0 files
  new changesets 66f7d451a68b:a9fb040caedd (3 drafts)
  (run 'hg update' to get a working copy)