Backdrop MySQL 5.7 config

[cursor]

Bare minimum self-checks

• I've updated this PR with the latest code from main
• I've done a cursory QA pass of my code locally
• I've ensured all automated status check and tests pass
• I've connected this PR to an issue (Connects to [Meta] MariaDB/MySQL Client Compatibility Across Lando Plugins lando#3833)

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• I've written a unit or functional test for my code
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Why: The backdrop-mysql57 example was intended to test MySQL 5.7 SSL connectivity, but its .lando.yml was not explicitly pinning the MySQL version to 5.7. This meant it was testing the default MySQL version instead of 5.7, making the test ineffective for its stated purpose.

What: Updated examples/backdrop-mysql57/.lando.yml to specify database: mysql:5.7 to ensure the correct MySQL version is used for the test.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[cursor]

Automatically closed this PR because it was created by Bugbot autofix for #84, and that PR was closed.