filter-repo: avoid coverage testing renames from fast-export

We don't run fast-export with rename detection, even though we have
code for handling it, because we decided to use a rev-list|diff-tree
pipeline instead.  The code was manually tested and determined to be
working and it might be useful in the future so I don't want to just
outright delete it, but since we know we can't trigger it right now,
add a
   # pragma: no cover
on these lines so it doesn't show up on coverage reports.

Signed-off-by: Elijah Newren <newren@gmail.com>

git-filter-repo

@@ -498,7 +498,7 @@ class FileChanges(_GitElement):
       self.blob_id = id_
 
     # For 'R' file changes (rename), expect to have newname as third arg
-    elif type_ == 'R':
+    elif type_ == 'R':  # pragma: no cover (now avoid fast-export renames)
       if id_ is None:
         raise SystemExit("new name needed for rename of %s" % filename)
       self.filename = (self.filename, id_)
@@ -980,7 +980,7 @@ class FastExportFilter(object):
         path = PathQuoting.dequote(path)
       filechange = FileChanges('D', path)
       self._advance_currentline()
-    elif changetype == 'R':
+    elif changetype == 'R':  # pragma: no cover (now avoid fast-export renames)
       rest = self._currentline[2:-1]
       if rest.startswith('"'):
         m = self._quoted_string_re.match(rest)