chore: track OpenZeppelin Sepolia upgrade manifest

Add a .gitignore exception for unknown-11155111.json so the OpenZeppelin
manifest is versioned like mainnet layout history, avoiding "Manifest not
found" on fresh clones when running Sepolia upgrades.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: lionakhnazarov

.gitignore

@@ -19,6 +19,7 @@ yarn-error.log
 
 # OpenZeppelin
 .openzeppelin/unknown-*.json
+!.openzeppelin/unknown-11155111.json
 
 # Generated operator setup artifacts
 operator-*-keystore/