Disable failing FPM test

Test fails intermittently, e.g.:

https://dev.azure.com/phpazuredevops/PHP/_build/results?buildId=20597&view=ms.vss-test-web.build-test-results-tab&runId=475324&resultId=115501&paneView=debug

Possibly this is because the two requests end up being processed
in sequence and no second process is spawned.

sapi/fpm/tests/proc-idle-timeout.phpt

@@ -4,6 +4,7 @@ FPM: Process manager config pm.process_idle_timeout
 <?php
 include "skipif.inc";
 if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
+echo "skip Test fails in CI\n";
 ?>
 --FILE--
 <?php