Toolchain tests are not executed

The `src/it/multirelease-patterns/singleproject-toolchains` integration test is never executed, neither locally or by GitHub Actions (GHA), because it requires a specific configuration: Java 8, Java 10 and Java 17 installed on the machine and configured in `~/.m2/toolchains.xml`. I don't think that the current configuration of GHA meets these requirement. At least, I verified in the logs that the `singleproject-toolchains` test is skipped by GHA.

This test is a bit orphan for now. Re-enabling this test would require knowledge of GHA and Toolchain, and to find a way to keep them synchronized. I.e.: if GHA is updated with new Java versions, find a way to ensure that `singleproject-toolchains` is also updated.

This issue replace #1098.

Start with src/it/multirelease-patterns/singleproject-toolchains and the GitHub Actions configuration, then compare their Java requirements with ~/.m2/toolchains.xml. Check the GHA logs and local integration-test setup first; done means the test executes in both environments and its configured Java versions remain synchronized with GHA.

Written by the indexing model from the issue text.