t9210: pass safe.bareRepository=all to scalar register

This test expects `scalar register` to discover a bare repo and
reject it. Since `scalar` does not support `--git-dir` (that option
would not make sense in the context of that command), pass `-c
safe.bareRepository=all` to opt into implicit discovery of bare
repositories, so the test keeps working once the default changes to
`explicit`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

t/t9210-scalar.sh

@@ -88,7 +88,7 @@ test_expect_success 'scalar enlistments need a worktree' '
 	test_when_finished rm -rf bare test &&
 
 	git init --bare bare/src &&
-	! scalar register bare/src 2>err &&
+	! scalar -c safe.bareRepository=all register bare/src 2>err &&
 	grep "Scalar enlistments require a worktree" err &&
 
 	git init test/src &&