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
$ echo 0 > a
$ hg ci -qAm 0
$ for i in 5 8 14 43 167; do
> hg up -q 0
> echo $i > a
> hg ci -qm $i
> done
$ cat <<EOF >> .hg/hgrc
> [alias]
> l = log -T '{rev}:{shortest(node,1)}\n'
> EOF
$ hg l
5:00f
4:7ba5d
3:7ba57
2:72
1:9
0:b
$ cat <<EOF >> .hg/hgrc
> [experimental]
> revisions.disambiguatewithin=not 4
> EOF
$ hg l
5:00
4:7ba5d
3:7b
2:72
1:9
0:b
9 was unambiguous and still is
$ hg l -r 9
1:9
7 was ambiguous and still is
$ hg l -r 7
abort: 00changelog.i@7: ambiguous identifier!
[255]
7b is no longer ambiguous
$ hg l -r 7b
3:7b
$ cd ..