Don't clear isCommitStateDirty flag in setReadOnly (#1842)

When autoCommit is false, if setReadOnly is called after some queries, then closing the connection leads to dirty (transaction opened) connection being reused.

src/main/java/com/zaxxer/hikari/pool/ProxyConnection.java

@@ -430,7 +430,6 @@ public abstract class ProxyConnection implements Connection
    {
       delegate.setReadOnly(readOnly);
       isReadOnly = readOnly;
-      isCommitStateDirty = false;
       dirtyBits |= DIRTY_BIT_READONLY;
    }
 

src/test/java/com/zaxxer/hikari/pool/ConnectionStateTest.java

@@ -164,6 +164,9 @@ public class ConnectionStateTest
 
             resultSet.updateRow();
             assertTrue(TestElf.getConnectionCommitDirtyState(connection));
+
+            connection.setReadOnly(!connection.isReadOnly());
+            assertTrue(TestElf.getConnectionCommitDirtyState(connection));
          }
       }
    }