Apply suggestions from code review

Co-authored-by: Markus Scherer <markus.icu@gmail.com>

.github/workflows/cache_retain.yml

@@ -1,4 +1,4 @@
-# Copyright (C) 2016 and later: Unicode, Inc. and others.
+# Copyright (C) 2023 and later: Unicode, Inc. and others.
 # License & terms of use: http://www.unicode.org/copyright.html
 #
 # This workflow is designed to keep specific caches on the main
@@ -9,11 +9,11 @@
 # constructing the cache.
 #
 # Preventing a cache from eviction using this workflow requires that:
-#  - the cache is not too big that is starves other caches 
+#  - the cache is not too big that it starves other caches 
 #    from using the shared cache quota for the repository
 #  - the cache key is specific enough to avoid cache collisions, according
 #    to good cache key design
-#  - the cache key is not overly specific to cache unnecessary cache misses
+#  - the cache key is not overly specific to cause unnecessary cache misses
 #    (resulting in duplicate caches values, thereby wasting space), according
 #    to good cache key design
 #  - For more details, see: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows