t: prepare git config --unset calls for set -e

We have a couple of calls to `git config --unset` that ultimately end up
as no-ops as the configuration variables aren't set (anymore) in the
first place. These calls are mostly intended to recover unconditionally
from tests that may have executed only partially, but they'll ultimately
fail during a normal test run.

This hasn't been a problem until now as we aren't running tests with
`set -e`. This is about to change though, so let's silence the case
where we cannot unset the config keys.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

t/t4032-diff-inter-hunk-context.sh

@@ -17,7 +17,7 @@ f() {
 
 t() {
 	use_config=
-	git config --unset diff.interHunkContext
+	git config --unset diff.interHunkContext || :
 
 	case $# in
 	4) hunks=$4; cmd="diff -U$3";;

t/t7508-status.sh

@@ -773,8 +773,8 @@ test_expect_success TTY 'status --porcelain ignores color.status' '
 '
 
 # recover unconditionally from color tests
-git config --unset color.status
-git config --unset color.ui
+git config --unset color.status || :
+git config --unset color.ui || :
 
 test_expect_success 'status --porcelain respects -b' '
 

t/t9138-git-svn-authors-prog.sh

@@ -68,8 +68,8 @@ test_expect_success 'authors-file overrode authors-prog' '
 	)
 '
 
-git --git-dir=x/.git config --unset svn.authorsfile
-git --git-dir=x/.git config --unset svn.authorsprog
+git --git-dir=x/.git config --unset svn.authorsfile || :
+git --git-dir=x/.git config --unset svn.authorsprog || :
 
 test_expect_success 'authors-prog imported user without email' '
 	svn mkdir -m gg --username gg-hermit "$svnrepo"/gg &&