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
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.