Fixing py lint errors

Bug: webrtc:9548
Change-Id: I0daf8dc06fdaac1637c32994ef6ad542ed52202a
Reviewed-on: https://webrtc-review.googlesource.com/90045
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Niklas Enbom <niklas.enbom@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24068}
diff --git a/presubmit_test.py b/presubmit_test.py
index 6f14999..d6e5129 100755
--- a/presubmit_test.py
+++ b/presubmit_test.py
@@ -237,7 +237,7 @@
     self.assertTrue('bar.c' in str(errors[0]))
 
   def _AssertNumberOfErrorsWithSources(self, number_of_errors, sources):
-    assert 3 == len(sources), 'This function accepts a list of 3 source files'
+    assert len(sources) == 3, 'This function accepts a list of 3 source files'
     self._GenerateBuildFile(textwrap.dedent("""
       rtc_static_library("bar_foo") {
         sources = [