Add commcare_core_status_sha input for cross-repo CI

[dannyroberts]

Technical Summary

Adds a new commcare_core_status_sha input to the cross-repo CI workflow dispatch.
This allows the commcare-core trigger workflow to send the merge commit SHA
(commcare_core_sha) for checkout — testing the same code commcare-core's own
build tested — while sending the PR head SHA (commcare_core_status_sha) for
reporting status back to the correct commit on the PR.

The status reporting step uses commcare_core_status_sha when provided, falling
back to commcare_core_sha for backward compatibility.

Cross-request: dimagi/commcare-core#1525

Safety Assurance

Safety story

Additive change — adds one optional input and adjusts which SHA is used for
status reporting. Existing behavior is unchanged when the new input is not provided.

Automated test coverage

CI infrastructure — validated by end-to-end testing.

QA Plan

Verified via cross-repo CI test runs.

Special deploy instructions

• This PR can be deployed after merge with no further considerations.

Rollback instructions

• This PR can be reverted after deploy with no further considerations.

Review

• The set of people pinged as reviewers is appropriate for the level of risk of the change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.21%. Comparing base (3ee2a65) to head (ec185e5).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1766   +/-   ##
=========================================
  Coverage     70.21%   70.21%           
  Complexity     2029     2029           
=========================================
  Files           257      257           
  Lines          7996     7996           
  Branches        761      761           
=========================================
  Hits           5614     5614           
  Misses         2099     2099           
  Partials        283      283           

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