update Batch module to be compatible with TPG v6

[RachaelSTamakloe]

This pr updates the instance_template submodule version used in Batch-job-template to be the following:

source  = "terraform-google-modules/vm/google//modules/instance_template"
  version = "~> 12.1"

Submission Checklist

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Please take the following actions before submitting this pull request.

• Fork your PR branch from the Toolkit "develop" branch (not main)
• Test all changes with pre-commit in a local branch #
• Confirm that "make tests" passes all tests
• Add or modify unit tests to cover code changes
• Ensure that unit test coverage remains above 80%
• Update all applicable documentation
• Follow Cluster Toolkit Contribution guidelines #

[tpdownes]

LGTM