Publish ampere-core-test-fixtures to Maven Central for real

[wow-miley]

Problem

ampere-core-test-fixtures (ampere-core-test-fixtures/build.gradle.kts:27, coordinates("link.socket", "ampere-core-test-fixtures", version.toString())) is declared for publishing and the 0.12.0 CHANGELOG entry (#638) says "published as its own Maven artifact" — but it is not actually reachable on Maven Central at any version:

$ curl -sI https://repo.maven.apache.org/maven2/link/socket/ampere-core-test-fixtures/0.12.0/ampere-core-test-fixtures-0.12.0.pom
HTTP/2 404

$ curl -sI https://repo.maven.apache.org/maven2/link/socket/ampere-core-test-fixtures/0.13.0/ampere-core-test-fixtures-0.13.0.pom
HTTP/2 404

ampere-core itself (the same publish pipeline, same version) is reachable at 0.13.0. So ampere-core-test-fixtures specifically is falling out somewhere between "declared for publishing" and "actually released."

How this was masked, and why that's worse

Socket (socket-link/socket) worked around the missing artifact by committing the built ampere-core-test-fixtures jars/klibs/aars for every platform target directly into its own repo at libs/repo/link/socket/ampere-core-test-fixtures* (first done in socket-link/socket#1115, commit fdd2584e) and pointing settings.gradle.kts at that folder as an extra Maven repository. That's 54 binary files checked into git standing in for a real release: unauditable, un-diffable, silently drifts from whatever ampere-core-test-fixtures source tag they supposedly correspond to, and has to be manually re-vendored by hand on every ampere-core version bump (which is exactly how the gap stayed invisible for two releases). This has now been removed from Socket's repo — Socket's build will not resolve ampere-core-test-fixtures again until this is fixed at the source.

Ask

Fix ampere-core's publish pipeline so ampere-core-test-fixtures actually lands on Maven Central alongside ampere-core for every release, starting with backfilling 0.13.0. Consumers should never need to vendor test-fixtures binaries into their own repo to get an internal dependency working.