test-mq-header: don't fail with different patch(1)

At least under FreeBSD patch(1) won't fail on empty patch and will print
'Hmm...' warning instead. Sanitize output so tests won't fail unexpectedly.

tests/test-mq-header-date

@@ -103,8 +103,7 b' hg qnew 5.patch'
 hg qpop
 echo "# HG changeset patch" >>.hg/patches/5.patch
 echo "# Date 10 0" >>.hg/patches/5.patch
-# Drop patch specific error line
-hg qpush 2>&1 | grep -v garbage
+hg qpush 2>&1 | grep 'Now at'
 catlogd 5
 
 echo ==== hg qref

tests/test-mq-header-date.out

@@ -129,9 +129,6 b' 0: [mq]: 1.patch - test'
 Now at: 3.patch
 ==== qnew with HG header
 Now at: 3.patch
-applying 5.patch
-patch failed, unable to continue (try -v)
-patch 5.patch is empty
 Now at: 5.patch
 # HG changeset patch
 # Date 10 0

tests/test-mq-header-from

@@ -83,8 +83,7 b' hg qnew 5.patch'
 hg qpop
 echo "# HG changeset patch" >>.hg/patches/5.patch
 echo "# User johndoe" >>.hg/patches/5.patch
-# Drop patch specific error line
-hg qpush 2>&1 | grep -v garbage
+hg qpush 2>&1 | grep 'Now at'
 catlog 5
 
 echo ==== hg qref

tests/test-mq-header-from.out

@@ -131,9 +131,6 b' 1: [mq]: 2.patch - jane'
 0: [mq]: 1.patch - mary
 ==== qnew with HG header
 Now at: 4.patch
-applying 5.patch
-patch failed, unable to continue (try -v)
-patch 5.patch is empty
 Now at: 5.patch
 # HG changeset patch
 # User johndoe