tests: make emacs test less strict
It was failing like this for me:
```
@@ -2,7 +2,7 @@
$ emacs -q -no-site-file -batch -l $TESTDIR/../contrib/hg-test-mode.el \
> -f ert-run-tests-batch-and-exit
Running 1 tests (*) (glob)
- passed 1/1 hg-test-mode--compilation-mode-support
+ passed 1/1 hg-test-mode--compilation-mode-support (0.045732 sec)
- Ran 1 tests, 1 results as expected (*) (glob)
+ Ran 1 tests, 1 results as expected, 0 unexpected (2020-09-11 16:49:56+0000, 0.046034 sec)
```
Differential Revision: https://phab.mercurial-scm.org/D9017
$ hg init repo
$ cd repo
$ touch foo
$ hg ci -Am 'add foo'
adding foo
$ hg up -C null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
this should be stored as a delta against rev 0
$ echo foo bar baz > foo
$ hg ci -Am 'add foo again'
adding foo
created new head
$ hg debugindex foo
rev linkrev nodeid p1 p2
0 0 b80de5d13875 000000000000 000000000000
1 1 0376abec49b8 000000000000 000000000000
$ cd ..