chore(deps): Bump mxschmitt/action-tmate from 3.19 to 3.21 (#560)

Bumps [mxschmitt/action-tmate](https://github.com/mxschmitt/action-tmate) from 3.19 to 3.21.
- [Release notes](https://github.com/mxschmitt/action-tmate/releases)
- [Changelog](https://github.com/mxschmitt/action-tmate/blob/master/RELEASE.md)
- [Commits](mxschmitt/action-tmate@e5c7151...c606f86)

---
updated-dependencies:
- dependency-name: mxschmitt/action-tmate
  dependency-version: '3.21'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/staging-db-publisher.yaml

@@ -71,7 +71,7 @@ jobs:
         # a) booleans come across as string types :(
         # b) if not using workflow_dispatch the default values are empty, which means we want these to effectively evaluate to true (so only check the negative case)
         if: github.event.inputs.run-tmate != 'false'
-        uses: mxschmitt/action-tmate@e5c7151931ca95bad1c6f4190c730ecf8c7dde48 #v3.19
+        uses: mxschmitt/action-tmate@c606f8612a802e46b3742322514c09fbc8c4afee #v3.21
         timeout-minutes: ${{ fromJSON(github.event.inputs.tmate-duration) }}
         with:
           limit-access-to-actor: true