JSpecify conformance test artifacts expired

I am running into resolution problems with conformance-tests, which is built from https://github.com/jspecify/jspecify/tree/main/conformance-tests:

A problem occurred evaluating root project 'jspecify-conformance'.
> Could not resolve all files for configuration ':jSpecifyConformanceTests'.
   > Could not resolve org.jspecify.conformance:conformance-tests:0.0.0-SNAPSHOT.
     Required by:
         root project 'jspecify-conformance'
      > Could not resolve org.jspecify.conformance:conformance-tests:0.0.0-SNAPSHOT.
         > Unable to load Maven meta-data from https://central.sonatype.com/repository/maven-snapshots/org/jspecify/conformance/conformance-tests/0.0.0-SNAPSHOT/maven-metadata.xml.
            > Could not HEAD 'https://central.sonatype.com/repository/maven-snapshots/org/jspecify/conformance/conformance-tests/0.0.0-SNAPSHOT/maven-metadata.xml'. Received status code 403 from server: Forbidden

and the conformance-test-framework, which is built from https://github.com/jspecify/jspecify-reference-checker/tree/main/conformance-test-framework

> Could not resolve all files for configuration ':testCompileClasspath'.
   > Could not find org.jspecify.conformance:conformance-test-framework:0.0.0-SNAPSHOT.
     Searched in the following locations:
       - https://central.sonatype.com/repository/maven-snapshots/org/jspecify/conformance/conformance-test-framework/0.0.0-SNAPSHOT/maven-metadata.xml
       - https://central.sonatype.com/repository/maven-snapshots/org/jspecify/conformance/conformance-test-framework/0.0.0-SNAPSHOT/conformance-test-framework-0.0.0-SNAPSHOT.pom
     Required by:
         root project 'jspecify-conformance'

The snapshot documentation states: "Specifically, -SNAPSHOT releases are cleaned up after a period of time (currently 90 days)."

In the jspecify repository there has been a more recent push, but not in the reference checker repository. I don't know why neither one seems to have artifacts now.

I'm now working around the failures by locally building the artifacts, which is relatively quick, but clearly not ideal.

At some point we had discussed separating the conformance test artifacts into a separate repository and then making a proper release. That would solve this issue.
An alternative is to publish the SNAPSHOT artifacts e.g. on a monthly basis, to ensure they remain available.

Start with the linked conformance-tests and conformance-test-framework repositories, then inspect how their Maven snapshot artifacts are published and how jspecify-conformance resolves them. Reproduce the failed dependency resolution and review the workaround in PR 141. Done means the conformance artifacts remain available through a documented publication process without requiring local builds.