opcache: file_cache_read_only code review update 6 (#16484)

Author: iamacarpet

UPGRADING

@@ -108,11 +108,10 @@ PHP 8.5 UPGRADE NOTES
 - Opcache:
   . Introduce opcache.file_cache_read_only to support a read-only
     opcache.file_cache directory, for use with read-only Docker containers.
-    Best used with `opcache.validate_timestamps=0`, `opcache.revalidate_freq=0`
-    and `opcache.enable_file_override=1`.
-    Note: this cache isn't portable between PHP builds, enforced by the
-    inclusion of the `zend_system_id` both in the directory path, and
-    each cache file.
+    Best used with `opcache.validate_timestamps=0`, `opcache.enable_file_override=1`
+    and `opcache.file_cache_consistency_checks=false`.
+    Note: A cache generated with a different build of PHP, or different settings
+    (including which extensions are loaded) may be ignored.
 
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 10. New Global Constants