test-lib: add missing prerequisites for Darwin

commit d3d8c60 ("t7815: fix unexpectedly passing test on macOS",
2025-06-02) added a MACOS prerequisite by adding a 'Darwin' case
label to the 'OS-specific' case statement. However, this commit
forgot to set several prerequisites which appear in the 'default'
case label, in addition to the new MACOS prerequisite. This causes
several tests, which macOS should pass, being skipped.

In order to run all applicable tests on macOS, add the missing
prerequisites to the 'Darwin' case.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ramsay-jones

t/test-lib.sh

@@ -1645,6 +1645,9 @@ uname_s=$(uname -s)
 case $uname_s in
 Darwin)
 	test_set_prereq MACOS
+	test_set_prereq POSIXPERM
+	test_set_prereq BSLASHPSPEC
+	test_set_prereq EXECKEEPSPID
 	;;
 *MINGW*)
 	# Windows has its own (incompatible) sort and find