Test hardened ITensorActions workflows

[mtfishman]

Summary

This PR is a workflow canary for the hardened reusable workflows in ITensorActions PR #88.

It updates the SparseArraysBase workflow callers to point at the ITensorActions PR head SHA so we can validate the new behavior before doing a broader ecosystem sweep:

• switch IntegrationTest.yml from pull_request_target to pull_request
• use the new IntegrationTest pkgs JSON-array input, keeping one package per line for readable YAML diffs
• switch FormatCheck.yml from pull_request_target to pull_request
• add FormatCheckComment.yml for the trusted comment-writing step
• point /integrationtest at the same ITensorActions test SHA and grant the check-writing permissions it needs

Canary Note

FormatCheck.yml sets concurrent-jobs: true only for this canary. The old default-branch pull_request_target Format Check still exists while this PR is open, and otherwise cancels the new pull_request run through the shared concurrency group. This line is not necessarily part of the eventual ecosystem sweep.

Validation Goal

This PR should validate the public-package IntegrationTest matrix and the read-only FormatCheck parse phase on a normal same-repo PR. The workflow_run-based comment workflow is included here, but full comment-writing validation may require a follow-up PR after this workflow exists on the default branch.

Test Plan

• Let GitHub Actions run on this PR.
• Confirm the aggregate IntegrationTest check passes for the public downstream matrix.
• Confirm Format Check / Check Formatting runs from pull_request without trusted write permissions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.68%. Comparing base (56815b3) to head (c2df0fd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #173   +/-   ##
=======================================
  Coverage   78.68%   78.68%           
=======================================
  Files          12       12           
  Lines         793      793           
=======================================
  Hits          624      624           
  Misses        169      169           

Flag	Coverage Δ
docs	30.20% <ø> (ø)

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