[test] Make printing the list of processes Python3 compatible

Bug: v8:13101
Change-Id: I5d144939b420957eab58ead64836b561bd541a00
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3784601
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81918}

tools/testrunner/testproc/util.py

@@ -22,7 +22,7 @@ def list_processes_linux():
     return []
   try:
     cmd = 'pgrep -fa %s' % OUT_DIR
-    output = subprocess.check_output(cmd, shell=True) or ''
+    output = subprocess.check_output(cmd, shell=True, text=True) or ''
     processes = [
       (int(line.split()[0]), line[line.index(OUT_DIR):])
       for line in output.splitlines()