chore: converge Renovate preset and migrate deprecated manager config

Andrew Dunnrequested to merge
andunn-renovate-converge-preset into main

What

  • Update the shared-preset reference to gitlab>gitlab-com/public-sector/pipeline:renovate-config.
  • Migrate the deprecated fileMatch key on the custom manager to managerFilePatterns.

Why

The previous preset reference used a subdirectory compatibility shim; this points at the canonical preset directly. The fileMatch key is deprecated in current Renovate. Manager behavior is unchanged: the KANIKO_VERSION and GO_VERSION pins continue to be tracked, and the kaniko-upstream grouping with automerge: false is preserved.

Validation

Validated with renovate-config-validator --strict.

DO NOT MERGE pending human review.

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