filter-repo: ensure we close files so they get written

It appears that python will usually write out files even if we do not
explicitly close them, but other tweaks to the code can make this not
happen.  Explicitly close the files to be safe.

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

git-filter-repo

@@ -2666,6 +2666,10 @@ class InputFileBackup:
     self.input_file  = input_file
     self.output_file = output_file
 
+  def close(self):
+    self.input_file.close()
+    self.output_file.close()
+
   def read(self, size):
     output = self.input_file.read(size)
     self.output_file.write(output)
@@ -3896,6 +3900,7 @@ class RepoFilter(object):
       # Make sure fast-export completed successfully
       if not self._args.stdin and self._fep.wait():
         raise SystemExit(_("Error: fast-export failed; see above.")) # pragma: no cover
+      self._input.close()
 
     # If we're not the manager of self._output, we should avoid post-run cleanup
     if not self._managed_output: