chore: rename column in post-validation script

[jvbriones]

---

Note

Renames the tests column and standardizes Sheets to 8 columns while adding fallback to use tabs without the "pre-" prefix.

• .github/scripts/post-merge-validation-tracker.mjs:
  • Sheets structure:
    • Rename header from Auto Tests to Tests changes? and reduce columns to 8 (A..H).
    • Update all ranges from ...!A2:I2, A3:I, A4:I to ...!A2:H2, A3:H, A4:H.
    • Remove extra trailing empty column in inserted rows.
  • Tab resolution:
    • Enhance ensureSheetExists to return actualTitle and detect tabs renamed without the pre- prefix.
    • Update logging and read/append operations to use actualTitle.

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