Auto merge of #27005 - saschanaz:py3-tidy, r=jdm

Do not raise StopIteration: PEP 479

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This fixes `test-tidy` Py3 compatibility, as [PEP 479](https://www.python.org/dev/peps/pep-0479/) says `return` must be used to stop iteration inside generator instead of `raise StopIteration`.

This introduces subtle behavior change where `FileList()` constructor now won't implicitly stop the caller generator when the list is empty. `wpt_lint.py` is modified to explicitly stop when empty, to match the change.

---
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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python/servo/lints/wpt_lint.py

@@ -33,11 +33,13 @@ class Lint(LintRunner):
 
         wpt_working_dir = os.path.abspath(os.path.join(WPT_PATH, "web-platform-tests"))
         for suite in SUITES:
-            files = self._get_wpt_files(suite)
+            files = list(self._get_wpt_files(suite))
+            if not files:
+                continue
             sys.path.insert(0, wpt_working_dir)
             from tools.lint import lint
             sys.path.remove(wpt_working_dir)
             file_dir = os.path.abspath(os.path.join(WPT_PATH, suite))
-            returncode = lint.lint(file_dir, list(files), output_format="json")
+            returncode = lint.lint(file_dir, files, output_format="json")
             if returncode:
                 yield ("WPT Lint Tool", "", "lint error(s) in Web Platform Tests: exit status %s" % returncode)