tests: skip tests if strace is not functional

Chances are that strace is available but not functional due to
restricted permissions:

strace: test_ptrace_get_syscall_info: PTRACE_TRACEME: Operation not permitted
strace: ptrace(PTRACE_TRACEME, ...): Operation not permitted
+++ exited with 1 +++

Just skip the tests then.

Signed-off-by: Christian Hesse <mail@eworm.de>

tests/t0109-gitconfig.sh

@@ -9,6 +9,12 @@ test -n "$(which strace 2>/dev/null)" || {
 	exit
 }
 
+strace true 2>/dev/null || {
+	skip_all='Skipping access validation tests: strace not functional'
+	test_done
+	exit
+}
+
 test_no_home_access () {
 	non_existent_path="/path/to/some/place/that/does/not/possibly/exist"
 	while test -d "$non_existent_path"; do