Fix CodeCov upload issues (#1648)

Disable codecov binary validation which seems to be constantly failing

```
gpg: Signature made Tue Apr 21 19:28:03 2026 UTC
gpg:                using RSA key 27034E7FDB850E0BBC2C62FF806BB28AED779869
gpg: Can't check signature: No public key
==> Could not verify signature. Please contact Codecov if problem continues
    Exiting...
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
  * Updated CI workflow notes and removed an outdated header comment.
* Added explanatory comments to the Linux job and adjusted the code
coverage upload step to use a relaxed validation mode (no other upload
settings changed).
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Keval Morabia <28916987+kevalmorabia97@users.noreply.github.com>

.github/workflows/unit_tests.yml

@@ -1,4 +1,3 @@
-# NOTE: Make sure this file is consistent with .gitlab/tests.yml
 name: Unit tests
 
 on:
@@ -73,6 +72,10 @@ jobs:
           token: ${{ secrets.CODECOV_TOKEN }}
           flags: unit
           fail_ci_if_error: true
+          # Skip GPG/SHASUM integrity check of the Codecov CLI: its key import
+          # intermittently fails (codecov/codecov-action#1876), which would
+          # otherwise hard-fail this required job on a transient infra blip.
+          skip_validation: true
           verbose: true
   windows:
     if: needs.check-file-changes.outputs.any_changed == 'true'