Plugin POM hard-codes EE 8

[basil]

plugin-pom/pom.xml

Lines 182 to 187 in 8561e2e

	<dependency>
	<!-- used in JTH and jenkins core > 2.x -->
	<groupId>jakarta.servlet</groupId>
	<artifactId>jakarta.servlet-api</artifactId>
	<version>4.0.4</version>
	</dependency>

hard-codes the Servlet API to EE 8 (the last version with javax imports), which means that when core is upgraded to EE 9 and plugins upgrade their core baseline to that version, their tests will start failing, even if they have been otherwise prepared with a test harness that supports both EE 8 and EE 9 (see jenkinsci/jenkins-test-harness#770). This manifests in strange and hard-to-debug errors, like not being able to import jakarta servlet types, or the compatibility methods introduced in jenkinsci/javax-servlet-api#5 not existing (because the wrong javax version of the jakarta.servlet-api takes precedence over the package delivering the compatibility methods).

The ideal solution is to simply delete these lines and let the version be managed by the core (not plugin) BOM, which is possible as of jenkinsci/jenkins#9288; however, it would imply raising the minimum core version supported by this repository to 2.459 or higher, something that is likely too aggressive at this point in time.