Clarify Selenium auto-configuration requires HtmlUnit

The auto-configuration requires `HtmlUnit`, so this auto-cofiguration
only works if both Selenium and HtmlUnit are used.

Prevents misinterpretation that WebDriver can be auto configured without
htmlunit.

See gh-27920

Author: cdalexndr

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

@@ -7464,7 +7464,7 @@ The following example uses `MockMvc`:
 
 TIP: If you need to configure elements of the auto-configuration (for example, when servlet filters should be applied) you can use attributes in the `@AutoConfigureMockMvc` annotation.
 
-If you use HtmlUnit or Selenium, auto-configuration also provides an HtmlUnit `WebClient` bean and/or a Selenium `WebDriver` bean.
+If you use HtmlUnit and Selenium, auto-configuration also provides an HtmlUnit `WebClient` bean and/or a Selenium `WebDriver` bean.
 The following example uses HtmlUnit:
 
 [source,java,indent=0]