Disable SKC weekly upstream sync

[Alex-Welsh]

This reverts commit dc79b8d to disable the SKC weekly sync. The sync doesn't work and we haven't found time to fix it yet. Disabling it again until we do.

See also stackhpc/stackhpc-kayobe-config#2456

Summary by CodeRabbit

• Chores
  • Updated workflow settings to ignore the upstream-sync workflow on the default branch.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 21a675ec-3445-4bcf-a287-24572b0550b9

📥 Commits

Reviewing files that changed from the base of the PR and between c595126 and 7cb0acd.

📒 Files selected for processing (1)

• ansible/inventory/group_vars/all/source-repositories

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📝 Walkthrough

Walkthrough

Changes

Workflow configuration

Layer / File(s)	Summary
Add upstream-sync ignore rule ansible/inventory/group_vars/all/source-repositories	Adds upstream-sync to the default_branch_only ignored workflows for stackhpc-kayobe-config.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Suggested reviewers: dougszumski, mnasiadka, bbezak

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: disabling the SKC weekly upstream sync workflow.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch disable-skc-sync

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