test-bookmarks-pushpull: use correct tmp dir for no-bm-move.sh

test-bookmarks-pushpull.t writes a temporary file in $TESTDIR instead of
$TESTTMP.  Make it use $TESTTMP instead.

Differential Revision: https://phab.mercurial-scm.org/D5057

tests/test-bookmarks-pushpull.t

@@ -1231,13 +1231,13 b' Test that pre-pushkey compat for bookmar'
 
 Forbid bookmark move on the server
 
-  $ cat << EOF >> $TESTDIR/no-bm-move.sh
+  $ cat << EOF >> $TESTTMP/no-bm-move.sh
   > #!/bin/sh
   > echo \$HG_NAMESPACE | grep -v bookmarks
   > EOF
   $ cat << EOF >> server/.hg/hgrc
   > [hooks]
-  > prepushkey.no-bm-move= sh $TESTDIR/no-bm-move.sh
+  > prepushkey.no-bm-move= sh $TESTTMP/no-bm-move.sh
   > EOF
 
 pushing changeset is okay