Exclude firefox/welcome pages from sitemap (Fixes #7833)

bedrock/settings/base.py

@@ -266,6 +266,7 @@ SUPPORTED_NONLOCALES = [
 # specific URLs, add them to mozorg/templates/mozorg/robots.txt.
 NOINDEX_URLS = [
     r'^(404|500)/',
+    r'^firefox/welcome/',
     r'^contribute/(embed|event)/',
     r'^csp-violation-capture',
     r'^firefox/sms/sent/',