DM-54043: Use cached mysql image in TAP_SCHEMA Docker build

[JeremyMcCormick]

Checklist

When making changes to YAML files in the schemas directory:

• If applicable, incremented the schema version number, following the guidelines in the contribution guide
• Referred to the documentation on specific schemas for additional versioning information, change constraints, or tasks that may need to be performed, based on which schema is being updated
• Ran Jenkins
• Added a news fragment describing the changes

[JeremyMcCormick]

This seems to have been dealt with sufficiently by #462.