tests: fix test-convert-git to work w/ "git pull" requiring strategy

A recent change to git (031e2f7ae195) made it an error to not specify a strategy
(`--rebase`, `--no-rebase`, `--ff-only`), instead of just the warning it was
previously. As far as I can tell, `--no-rebase` is the behavior we were getting
before, and the only one that makes the test work.

Differential Revision: https://phab.mercurial-scm.org/D11714

tests/test-convert-git.t

@@ -50,7 +50,7 b' Remove the directory, then try to replac'
   $ echo a >> a
   $ commit -a -m t4.2
   $ git checkout master >/dev/null 2>/dev/null
-  $ git pull --no-commit . other > /dev/null 2>/dev/null
+  $ git pull --no-commit . other --no-rebase > /dev/null 2>/dev/null
   $ commit -m 'Merge branch other'
   $ cd ..
   $ hg convert --config extensions.progress= --config progress.assume-tty=1 \
@@ -137,7 +137,7 b' Remove the directory, then try to replac'
   $ git add baz
   $ commit -a -m 'add baz'
   $ git checkout master >/dev/null 2>/dev/null
-  $ git pull --no-commit . Bar Baz > /dev/null 2>/dev/null
+  $ git pull --no-commit . Bar Baz --no-rebase > /dev/null 2>/dev/null
   $ commit -m 'Octopus merge'
   $ echo bar >> bar
   $ commit -a -m 'change bar'
@@ -145,7 +145,7 b' Remove the directory, then try to replac'
   $ echo >> foo
   $ commit -a -m 'change foo'
   $ git checkout master >/dev/null 2>/dev/null
-  $ git pull --no-commit -s ours . Foo > /dev/null 2>/dev/null
+  $ git pull --no-commit -s ours . Foo --no-rebase > /dev/null 2>/dev/null
   $ commit -m 'Discard change to foo'
   $ cd ..
   $ glog()