Add semver to Dependabot ignore directives

[jsf9k]

🗣 Description

This pull request adds semver to the (commented-out) Dependabot ignore directives.

💭 Motivation and context

This was somehow missed in #188.

🧪 Testing

All automated tests pass.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.

[Copilot]

Pull request overview

This PR updates the repository’s Dependabot configuration to include semver in the (currently commented-out) ignore directives intended for downstream projects that inherit dependency management from the Lineage parent repo.

Changes:

• Add a commented-out Dependabot ignore entry for the Python dependency semver.

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[jsf9k]

I am an idiot. cisagov/skeleton-generic#264 will get merged and trickle down here.