ci: docker `latest` tag should only update for master branch

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72.40%. Comparing base (3e2d524) to head (8008bb1).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1971 +/- ## ======================================== Coverage 72.40% 72.40% ======================================== Files 94 94 Lines 12572 12572 Branches 2930 2925 -5 ======================================== Hits 9103 9103 Misses 3306 3306 Partials 163 163 ```

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[github-actions[bot]]

Vercel deployment URL: https://stacks-blockchain-2chbtdszx-blockstack.vercel.app :rocket:

[blockstack-devops]

:tada: This PR is included in version 7.11.0-beta.7 :tada:

The release is available on:

• npm package (@beta dist-tag)
• npm package (@beta dist-tag)
• GitHub release

Your semantic-release bot :package::rocket:

[blockstack-devops]

:tada: This PR is included in version 7.11.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: