chore: added changelog for 9793 (secp256r1 tx malleability) (cosmos#9796

)

## Description

Added missing changelog and updated a `p256Order` comment to remove misleading part.

---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [x] 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))
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- [x] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [x] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [x] added a changelog entry to `CHANGELOG.md`
- [x] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [x] updated the relevant documentation or specification
- [x] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] 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)

CHANGELOG.md

@@ -88,6 +88,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (x/genutil) [\#9638](https://github.com/cosmos/cosmos-sdk/pull/9638) Added missing validator key save when recovering from mnemonic
 * (server) [#9704](https://github.com/cosmos/cosmos-sdk/pull/9704) Start GRPCWebServer in goroutine, avoid blocking other services from starting.
 * [\#9762](https://github.com/cosmos/cosmos-sdk/pull/9762) The init command uses the chain-id from the client config if --chain-id is not provided
+* [\#9793](https://github.com/cosmos/cosmos-sdk/pull/9793) Fixed ECDSA/secp256r1 transaction malleability.
 
 ### State Machine Breaking
 

crypto/keys/internal/ecdsa/privkey.go

@@ -12,13 +12,7 @@ import (
 // p256Order returns the curve order for the secp256r1 curve
 // NOTE: this is specific to the secp256r1/P256 curve,
 // and not taken from the domain params for the key itself
-// (which would be a more generic approach for all EC)
-// In *here* we don't need to do it as a method on the key
-// since this code is only called for secp256r1
-// if called on a key:
-// func (sk PrivKey) pCurveOrder() *.big.Int {
-//     return sk.Curve.Params().N
-// }
+// (which would be a more generic approach for all EC).
 var p256Order = elliptic.P256().Params().N
 
 // p256HalfOrder returns half the curve order