tests: using custom GIT_EXEC_PATH breaks --valgrind tests

Fix a regression in b7d11a0 (tests: exercise the RUNTIME_PREFIX
feature, 2021-07-24) where tests that want to set up and test a "git"
wrapper in $PATH conflicted with the t/bin/valgrind wrapper(s) doing
the same.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0060-path-utils.sh

@@ -542,15 +542,15 @@ test_lazy_prereq CAN_EXEC_IN_PWD '
 	./git rev-parse
 '
 
-test_expect_success RUNTIME_PREFIX,CAN_EXEC_IN_PWD 'RUNTIME_PREFIX works' '
+test_expect_success !VALGRIND,RUNTIME_PREFIX,CAN_EXEC_IN_PWD 'RUNTIME_PREFIX works' '
 	mkdir -p pretend/bin pretend/libexec/git-core &&
 	echo "echo HERE" | write_script pretend/libexec/git-core/git-here &&
 	cp "$GIT_EXEC_PATH"/git$X pretend/bin/ &&
 	GIT_EXEC_PATH= ./pretend/bin/git here >actual &&
 	echo HERE >expect &&
 	test_cmp expect actual'
 
-test_expect_success RUNTIME_PREFIX,CAN_EXEC_IN_PWD '%(prefix)/ works' '
+test_expect_success !VALGRIND,RUNTIME_PREFIX,CAN_EXEC_IN_PWD '%(prefix)/ works' '
 	mkdir -p pretend/bin &&
 	cp "$GIT_EXEC_PATH"/git$X pretend/bin/ &&
 	git config yes.path "%(prefix)/yes" &&

t/test-lib.sh

@@ -1666,6 +1666,7 @@ test -n "$USE_LIBPCRE2" && test_set_prereq PCRE
 test -n "$USE_LIBPCRE2" && test_set_prereq LIBPCRE2
 test -z "$NO_GETTEXT" && test_set_prereq GETTEXT
 test -n "$SANITIZE_LEAK" && test_set_prereq SANITIZE_LEAK
+test -n "$GIT_VALGRIND_ENABLED" && test_set_prereq VALGRIND
 
 if test -z "$GIT_TEST_CHECK_CACHE_TREE"
 then