ci(docs-infra): increase minimum a11y scores for various pages (angular#37899)

As part of our CI checks, we ensure the a11y score on certain angular.io
pages do not fall below some thresholds.

This commit increases these thresholds based on our current scores to
ensure we do not regress below current values.

PR Close angular#37899

Author: gkalpak

aio/scripts/test-aio-a11y.js

@@ -22,12 +22,12 @@ sh.set('-e');
 const MIN_SCORES_PER_PAGE = {
   '': 100,
   'api': 100,
-  'api/core/Directive': 90,
-  'cli': 91,
-  'cli/add': 91,
+  'api/core/Directive': 98,
+  'cli': 98,
+  'cli/add': 98,
   'docs': 100,
-  'guide/docs-style-guide': 88,
-  'start': 90,
+  'guide/docs-style-guide': 95,
+  'start': 97,
 };
 
 // Run