added more debug traces to debug a problem that only happens in ci (can't reproduce even when logged as jenkins-agent)

The error message is:
> ValueError: failed to find compilers/ifort/latest amongst available environment modules (set())

work related to [https://bugzilla.ipr.univ-rennes.fr/show_bug.cgi?id=3958]

iprbench/envmodules.py

@@ -22,6 +22,7 @@ def get_available_modules() -> Set[EnvModule]:
     # modules
     # null
     stdout = completed_process.stdout.decode('utf-8')
+    logging.debug('get_available_modules: stdout="%s"', stdout)
     for line in stdout.splitlines():
         logging.debug('available module line: "%s"', line)
         if not re.search(r'\:$', line):  # ignore the directories such as '/usr/share/modules/modulefiles:'