Fix key to datasource health indicator in reference doc

Closes gh-26268

Author: snicoll

spring-boot-project/spring-boot-docs/src/docs/asciidoc/production-ready-features.adoc

@@ -678,7 +678,7 @@ with the `key` listed in the table below.
 | {spring-boot-actuator-module-code}/couchbase/CouchbaseHealthIndicator.java[`CouchbaseHealthIndicator`]
 | Checks that a Couchbase cluster is up.
 
-| `datasource`
+| `db`
 | {spring-boot-actuator-module-code}/jdbc/DataSourceHealthIndicator.java[`DataSourceHealthIndicator`]
 | Checks that a connection to `DataSource` can be obtained.