Test content generation with git diff return value

Rather than trying to parse output of subprocess, just check the return
value.

Fix #3042

pelican/tests/test_pelican.py

@@ -55,27 +55,15 @@ def tearDown(self):
         super().tearDown()
 
     def assertDirsEqual(self, left_path, right_path):
-        out, err = subprocess.Popen(
+        proc = subprocess.Popen(
             ['git', '--no-pager', 'diff', '--no-ext-diff', '--exit-code',
              '-w', left_path, right_path],
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE
-        ).communicate()
+        )
 
-        def ignorable_git_crlf_errors(line):
-            # Work around for running tests on Windows
-            for msg in [
-                    "LF will be replaced by CRLF",
-                    "CRLF will be replaced by LF",
-                    "The file will have its original line endings"]:
-                if msg in line:
-                    return True
-            return False
-        if err:
-            err = '\n'.join([line for line in err.decode('utf8').splitlines()
-                             if not ignorable_git_crlf_errors(line)])
-        assert not out, out
-        assert not err, err
+        proc.wait()
+        assert proc.returncode == 0
 
     def test_order_of_generators(self):
         # StaticGenerator must run last, so it can identify files that