Remove slurm portion of dependabot config

[abbas1902]

The requirements.txt here is not actually used by slurm (https://github.com/GoogleCloudPlatform/slurm-gcp/blob/master/scripts/requirements.txt is the one that is actually used when building images). Removing it from dependabot's config so it no longer generates PRs to update the packages.

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• Fork your PR branch from the Toolkit "develop" branch (not main)
• Test all changes with pre-commit in a local branch #
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• 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 #

[mr0re1]

Please also update Makefile:install-dev-deps
and tools/cloud-build/images/test-runner/Dockerfile by pointing to right file in slurm-gcp repo.