Ignore stderr when retrieving remote revision

Keeps stdout and stderr separate in roll_chromium_deps.py when getting a
remote HEAD revision. This is a speculative fix for the autoroller
getting clearly incorrect (timestamp-like) revisions that are not seen
when running locally. ANGLE's equivalent keeps stdout and stderr
separate.

Bug: 452840620, b/465468828
Change-Id: Ifddb6979276895db3a70a77666843e4e1a35592f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/280560
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

Author: bsheedy-work

scripts/roll_chromium_deps.py

@@ -437,11 +437,7 @@ def _get_remote_head_revision(remote_url: str) -> str:
         remote_url,
         'HEAD',
     ]
-    proc = subprocess.run(cmd,
-                          check=True,
-                          text=True,
-                          stdout=subprocess.PIPE,
-                          stderr=subprocess.STDOUT)
+    proc = subprocess.run(cmd, check=True, capture_output=True, text=True)
     head_revision = proc.stdout.strip().split()[0]
     return head_revision