docs: Corrext tx multisign documentation example. (cosmos#10274)

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## Description

Closes: #XXXX

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The docs state:

> Signing with multiple signers is done with the `tx multisign` command.

Yet the examples use an incorrect `multisignsign`:
```shell
simd tx multisignsign ...
```


### Author Checklist

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- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
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- [ ] confirmed all CI checks have passed

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- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

docs/run-node/txs.md

@@ -61,12 +61,12 @@ For example, starting with the `unsigned_tx.json`, and assuming the transaction
 
 ```bash
 # Let signer1 sign the unsigned tx.
-simd tx multisignsign unsigned_tx.json signer_key_1 --chain-id my-test-chain --keyring-backend test > partial_tx_1.json
+simd tx multisign unsigned_tx.json signer_key_1 --chain-id my-test-chain --keyring-backend test > partial_tx_1.json
 # Now signer1 will send the partial_tx_1.json to the signer2.
 # Signer2 appends their signature:
-simd tx multisignsign partial_tx_1.json signer_key_2 --chain-id my-test-chain --keyring-backend test > partial_tx_2.json
+simd tx multisign partial_tx_1.json signer_key_2 --chain-id my-test-chain --keyring-backend test > partial_tx_2.json
 # Signer2 sends the partial_tx_2.json file to signer3, and signer3 can append his signature:
-simd tx multisignsign partial_tx_2.json signer_key_3 --chain-id my-test-chain --keyring-backend test > partial_tx_3.json
+simd tx multisign partial_tx_2.json signer_key_3 --chain-id my-test-chain --keyring-backend test > partial_tx_3.json
 ```
 
 ### Broadcasting a Transaction