Merge result step failed due to file content does not match

Due to an issue in coverage merge_script, there are .profdata files
left behind, and the merge result step does not know how to handle
that. This will cause the step to fail, and eventually affects
rebaseline tool.

Temporary change this to a warning.

Bug: 1349848
Change-Id: I7f85aee671d8c3e957765e9eff80aecd90d0f02b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3860507


Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#1040141}