scripts: fix the Signed-off-by:-prohibiting hook to actually work

* scripts/git-hooks/commit-msg: Fix new test: we're searching a
multi-line buffer, so add the //m modifier.

diff --git a/scripts/git-hooks/commit-msg b/scripts/git-hooks/commit-msg
index f867331..56286d4 100755 (executable)
--- a/scripts/git-hooks/commit-msg
+++ b/scripts/git-hooks/commit-msg
@@ -125,7 +125,7 @@ sub check_msg($$)
   $buf =~ m!https?://debbugs\.gnu\.org/(?:cgi/bugreport\.cgi\?bug=)?(\d+)!s
     and return "use shorter http://bugs.gnu.org/$1";
 
-  $buf =~ /^ *Signed-off-by:/i
+  $buf =~ /^ *Signed-off-by:/mi
     and return q(do not use "Signed-off-by:");
 
   return '';