fix postgres adapter migration extension creation which already exists at this point (#2188)

Author: web3gh

packages/adapter-postgres/migrations/20240318103238_remote_schema.sql

@@ -21,7 +21,7 @@ BEGIN
         FROM pg_extension
         WHERE extname = 'vector'
     ) THEN
-        CREATE EXTENSION vector
+        CREATE EXTENSION vector IF NOT EXISTS
         SCHEMA extensions;
     END IF;
 END $$;
@@ -33,7 +33,7 @@ BEGIN
         FROM pg_extension
         WHERE extname = 'fuzzystrmatch'
     ) THEN
-        CREATE EXTENSION fuzzystrmatch
+        CREATE EXTENSION fuzzystrmatch IF NOT EXISTS
         SCHEMA extensions;
     END IF;
 END $$;