xxhash: update to 0.8.4 - #30569

Checking PR #30569: xxhash: update to 0.8.4 (Formalities Audit)

✅ Pull request originates from a dedicated feature branch (xxhash-0.8.4)

Commit 4a00d46 - xxhash: update to 0.8.4:

✅ Author and committer identities are valid
✅ Commit is not a merge commit
✅ Commit subject layout and length are valid: "xxhash: update to 0.8.4"
✅ Commit description lines adhere to width formatting rules
✅ Commit contains a valid 'Signed-off-by:' line matching author or committer
⚠️ Warning: Commit is unsigned or cryptographic signature verification failed (Reason: unsigned). Signing commits is a recommended best practice for verifying identity, but is not mandatory.