fix autotest syntaxWarning error

Fixes SyntaxWarning: invalid escape sequence '\(',
intruducted from the last change

Change-Id: Ia74cd376089caa8a20ef79a8b91b68b1d8345b61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6576040
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Dan Harrington <harringtond@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1463483}
diff --git a/tools/autotest.py b/tools/autotest.py
index 15051b7..e1f76792 100755
--- a/tools/autotest.py
+++ b/tools/autotest.py
@@ -157,7 +157,7 @@
     '//third_party/rapidhash:rapidhash_fuzztests',
     '//ui/ozone:ozone_integration_tests',
 ]
-"""
+r"""
  You can run this command to find test targets that do not match these regexes,
  and use it to update _TEST_TARGET_ALLOWLIST.
 rg '^(instrumentation_test_runner|test)\("([^"]*)' -o -g'BUILD.gn' -r'$2' -N \