added 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

@@ -2,6 +2,7 @@ from typing import Set
 from pathlib import Path
 import subprocess
 import re
+import logging
 
 EnvModule = str  # eg compilers/ifort/latest
 
@@ -22,6 +23,7 @@ def get_available_modules() -> Set[EnvModule]:
     # null
     stdout = completed_process.stdout.decode('utf-8')
     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:'
             available_modules.add(EnvModule(line))
     return available_modules