fix typo "excute" (#21488)

Author: Oreoxmt

optimistic-transaction.md

@@ -31,7 +31,7 @@ sequenceDiagram
     client->>TiDB: begin
     TiDB->>PD: get ts as start_ts
 
-    loop excute SQL
+    loop execute SQL
         alt do read
             TiDB->>PD: get region from PD or cache
             TiDB->>TiKV: get data from TiKV or cache with start_ts
@@ -47,7 +47,7 @@ sequenceDiagram
 
     opt start 2PC
         TiDB-->>TiDB: for all keys need to write,choose first one as primary
-        TiDB->>PD: locate each key
+        TiDB->>PD: locate each key
         TiDB-->>TiDB: group keys by region to [](region,keys)
 
         opt prewrite with start_ts