chore(deps): update docker/build-push-action action to v4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
docker/build-push-action	action	major	v2 -> v4

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Release Notes

docker/build-push-action (docker/build-push-action)

### [`v4`](https://togithub.com/docker/build-push-action/compare/v3...v4) [Compare Source](https://togithub.com/docker/build-push-action/compare/v3...v4) ### [`v3`](https://togithub.com/docker/build-push-action/compare/v2...v3) [Compare Source](https://togithub.com/docker/build-push-action/compare/v2...v3)

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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• [ ] If you want to rebase/retry this PR, check this box

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[github-actions[bot]]

Test coverage for 80a37fb78a6196e4f1da7a2a1353e0beec2cf7c8

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py     190      0     68      1    99%   306->309
----------------------------------------------------------
TOTAL            190      0     68      1    99%

Static code analysis report

Run started:2023-08-11 10:53:00.104296

Test results:
    No issues identified.

Code scanned:
    Total lines of code: 1133
    Total lines skipped (#nosec): 0
    Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
    Total issues (by severity):
        Undefined: 0
        Low: 0
        Medium: 0
        High: 0
    Total issues (by confidence):
        Undefined: 0
        Low: 0
        Medium: 0
        High: 0
Files skipped (0):