ci: bump superfly/flyctl-actions from 1.5 to 1.6 (#766)

Bumps [superfly/flyctl-actions](https://github.com/superfly/flyctl-actions) from 1.5 to 1.6.
- [Release notes](https://github.com/superfly/flyctl-actions/releases)
- [Commits](superfly/flyctl-actions@1.5...1.6)

---
updated-dependencies:
- dependency-name: superfly/flyctl-actions
  dependency-version: '1.6'
  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/deploy-demo.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: superfly/flyctl-actions@1.5
+      - uses: superfly/flyctl-actions@1.6
         with:
           args: deploy
         env: