Update instructions for overriding Tika server URL

Fixed the method to override Tika server URL in Solr configuration.

Author: davisagli

docs/docs/how-to-guides/upgrade-cve-2025-66516.md

@@ -37,7 +37,7 @@ Then pull the new `ghcr.io/kitconcept/solr` image and restart your services. The
 - Configuration to use an external Tika 3.2.3 server (patched against CVE-2025-66516)
 
 By default, Solr will connect to the Tika server at `http://tika:9998`.
-You can override this using the `solr.tika.url` environment variable.
+You can override this using the `solr.tika.url` option, which can be passed to Solr using the SOLR_OPTS environment variable, like this: `SOLR_OPTS="-Dsolr.tika.url=http://tika-acceptance:9998"`.
 
 ## Users with Custom Solr Images