[test-only, draft] Pin snap to Go-1.25.14 exporter revisions (421/422)

[marceloneppel]

Draft — TEST ONLY. Not for merge; exists to validate the SSDLC flow against a Charmed PostgreSQL snap whose Go exporters are built with go1.25.14.

Change

refresh_versions.toml [snap.revisions] now pins the store revisions carrying the go1.25.14 exporter rebuilds, published to the branch channel 16/edge/pg-exporters-go125 of neppel/pg-exporters-go125:

• amd64: revision 421 (was 406)
• arm64: revision 422 (was 407)

charm_refresh installs the snap by revision, so the deployed workload picks up prometheus-postgres-exporter 0.15.0-1ubuntu0.7ppa1, golang-github-prometheus-community-pgbouncer-exporter 0.7.0-1ubuntu0.24.04.6ppa1 and prometheus-pgbackrest-exporter 0.17.0+ds1-0ubuntu0.24.04.4ppa1 — govulncheck on all six binaries: 0 vulnerabilities.

Companion draft PRs: canonical/charmed-postgresql-rock (rock packing the same snap channel) and canonical/postgresql-k8s-operator (OCI resource pointing at the test rock).

CI result: lint/unit/build ✓ both arches; ~90 integration jobs ran — 83 passed including all core scenarios (test_charm, test_async_replication, backups, TLS, password rotation) with revisions 421/422. The 7 failures (self_healing_3, async_replication_upgrade, stereo_mode, async_replication_backups_ceph, backups_pitr_aws) are juju-controller networking flakes (no route to host to the controller API), unrelated to the snap revision change.