fix: use official gtfs-validator v7.1.0 release tag instead of USED_BY_GBFS_VALIDATOR_JAVA

[jcpitre]

Summary

The extract-1password-secret action from MobilityData/gtfs-validator was referenced using a custom tag USED_BY_GBFS_VALIDATOR_JAVA that was created specifically for this project. This PR replaces that tag with the official v7.1.0 release tag which already exists in the gtfs-validator repository.

Changes

• .github/workflows/deploy-snapshot.yml: Replace @USED_BY_GBFS_VALIDATOR_JAVA with @v7.1.0
• .github/workflows/release.yml: Replace @USED_BY_GBFS_VALIDATOR_JAVA with @v7.1.0
• Updated the comment above the action usage to reflect the use of an official release tag

Why

Using an official release tag is better practice than a custom tag, as it ties the reference to a well-defined, versioned release of the gtfs-validator project.

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Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

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