why "Transaction references a signature that is unnecessary" warning, and value of 'isSigner' is false in IDL?

I was playing with counter program in program-example repo.

When run test, I got warning: Transaction references a signature that is unnecessary, only the fee payer and instruction signer accounts should sign a transaction., even though the contract method executed as expected.

The on-chain code is:

#[program]pub mod counter_anchor {    use super::*;        ...    pub fn increment(ctx: Context<Increment>) -> Result<()> {        msg!(" call increment +  ...");                ctx.accounts.counter.count = ctx.accounts.counter.count.checked_add(1).unwrap();        Ok(())    }    ....}    ...#[derive(Accounts)]pub struct Increment<'info> {    #[account(mut)]    pub counter: Account<'info, Counter>,}#[account]#[derive(InitSpace)]pub struct Counter {    count: u64,}

And my client js code is:

async function test_call_increase() {  let tx = await program.methods    .increment()    .accounts({      counter: counterKeypair.publicKey,    })    // .signers([payer.payer, counterKeypair])        .transaction();    let txHash = await sendAndConfirmTransaction(      provider.connection,      tx,      [wallet.payer, counterKeypair],  // <== Here, two signer, first one for pay gas.      { skipPreflight: true }      );}

Also , in target/types/counter_anchor.ts , its isSigner is false.

    {"name": "increment","accounts": [        {"name": "counter","isMut": true,"isSigner": false        }      ],"args": []    },

AFAIK, I should let counter account to participate signing as to change its account data.

Why it say that counter shouldn't appear in signer list? How to fix it?

Thanks.