Fix hamcrest versioning

Prior to this junit 4.x was bringing in hamcrest-core, causing https://github.com/jenkinsci/workflow-support-plugin/pull/220 to fail:

mvn dependency:tree | grep -B3 -A 2 hamcrest-core
[INFO] |  |  \- com.shapesecurity:salvation2:jar:3.0.1:test
[INFO] |  +- io.jenkins.lib:support-log-formatter:jar:1.2:test
[INFO] |  +- junit:junit:jar:4.13.2:test
[INFO] |  |  \- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] |  +- org.eclipse.jetty:jetty-security:jar:10.0.15:test
[INFO] |  |  \- org.eclipse.jetty:jetty-server:jar:10.0.15:test

See the docs: https://hamcrest.org/JavaHamcrest/distributables

Care must be taken when upgrading from Hamcrest 1.3 or earlier. Due to the change in packaging, the version conflict resolution that happens in dependency management tools won’t happen automatically. A common example is projects that depend upon JUnit 4. JUnit 4 declares a transitive dependency upon hamcrest-core-1.3.jar. Because hamcrest-core is not the same artifact as hamcrest, it will not be upgraded.

Amends https://github.com/jenkinsci/plugin-pom/pull/762

Testing done

I've tested with a snapshot version of the pom:

mvn dependency:tree | grep -B3  hamcrest-core
[INFO] +- org.jenkins-ci.main:jenkins-test-harness:jar:2025.v6f97169a_d6a_f:test
[INFO] |  +- io.jenkins.lib:support-log-formatter:jar:1.2:test
[INFO] |  +- junit:junit:jar:4.13.2:test
[INFO] |  |  \- org.hamcrest:hamcrest-core:jar:2.2:test

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jenkinsci / plugin-pom

Fix hamcrest versioning #785

Testing done