Use SIGTERM to terminate test-introspection

The test-introspection binary has a custom SIGINT handler that tells the
user to press Ctrl-C again to quit, thus it would require a *second*
SIGINT to actually terminate. However, getting the timing between both
in order for the handler to run is racy, so as an alternative, we just
send SIGTERM instead, which has no custom handler and thus quits
test-introspection as expected.

https://phabricator.apertis.org/T8377



Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

run-test.sh

@@ -82,7 +82,7 @@ test_service_introspection() {
     "${TESTBINDIR}/test-introspection" > "${test_log}" &
     TEST_INTROSPECTION_PID=$!
     _sleep 5
-    kill -INT ${TEST_INTROSPECTION_PID}
+    kill -TERM ${TEST_INTROSPECTION_PID}
     # Was the test successful?
     for pattern in "name: SetTarget" "name: NewTargetValue" \
         "name: GetTarget" "name: RetTargetValue" \