Change TestResult log from bytes to str (part 2)

Update one more TestResult instantiation to pass in the log as a string.

Change-Id: I1e9ffd978c404c47e8c2c3940ab2089051e4d311
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/110570
Reviewed-by: K. Moon <kmoon@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/testing/tools/test_runner.py b/testing/tools/test_runner.py
index 15c2d61..c7f8aa7 100644
--- a/testing/tools/test_runner.py
+++ b/testing/tools/test_runner.py
@@ -695,7 +695,9 @@
 
     if txt_data:
       return self.test_case.NewResult(
-          result_types.FAIL, log=txt_data, reason=f'{txt_path} should be empty')
+          result_types.FAIL,
+          log=txt_data.decode(errors='backslashreplace'),
+          reason=f'{txt_path} should be empty')
 
     return self.test_case.NewResult(result_types.PASS)