ci(release): fix invalid env context in the prebuilt workflow call

[ronaldtse]

Summary

• release.yml has failed with a workflow-file issue on every trigger since it was introduced - actionlint pinpoints it: the prebuilt job calls the reusable prebuilt.yml with tag: env.RELEASE_TAG, but the env context is not allowed in a caller's job-level with: (only github/needs/vars/inputs).
• Fixed by computing the tag with the allowed contexts - identical semantics to the workflow-level env definition the other jobs use.
• Verified locally: actionlint fails on the original file at exactly that line and passes with the fix.

Test plan

• actionlint/CI green
• next tag push or workflow dispatch of release.yml starts jobs instead of failing with a workflow file issue

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.46%. Comparing base (100cc8c) to head (c9bcd18).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2481   +/-   ##
=======================================
  Coverage   85.46%   85.46%           
=======================================
  Files         125      125           
  Lines       22962    22962           
=======================================
  Hits        19625    19625           
  Misses       3337     3337           

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[ronaldtse]

@ni4 one-line workflow fix for your class: release.yml has failed with a workflow-file issue on every trigger since it was introduced - the prebuilt job passes env.RELEASE_TAG to the reusable workflow, but the env context is not allowed in a caller's job-level with: (actionlint pinpoints the exact line). Now computed from the github/inputs contexts instead. All checks green except the known fuzzing exceptions.

[ni4]

LGTM! Merging with single approval as CI-only.