Close file handles for run_shell_cmd

The stdin/stdout/stderr handles need be closed by calling `communicate`.
Otherwise the handles will be leaked and e.g.
`test_run_shell_cmd_qa_trace` fails because it may capture a related
warning.

Author: Flamefire

easybuild/tools/run.py

@@ -580,8 +580,10 @@ def to_cmd_str(cmd):
         for line in iter(proc.stdout.readline, b''):
             _log.debug(f"Captured stdout: {line.decode(errors='ignore').rstrip()}")
             stdout += line
+        proc.stdout.close()
         if split_stderr:
             stderr += proc.stderr.read() or b''
+            proc.stderr.close()
     else:
         (stdout, stderr) = proc.communicate(input=stdin)