docs: fix typo in banker documentation (#1634)

## Description

This PR introduces a typo fix in the banker concept & reference pages.

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

docs/concepts/standard-library/banker.md

@@ -10,7 +10,7 @@ The Banker module can be cast into 4 subtypes of bankers that expose different f
 
 ### Banker Types
 
-1. `BankerTypeReadOnly` - read-only access to coin balances
+1. `BankerTypeReadonly` - read-only access to coin balances
 2. `BankerTypeOrigSend` - full access to coins sent with the transaction that called the banker
 3. `BankerTypeRealmSend` - full access to coins that the realm itself owns, including the ones sent with the transaction
 4. `BankerTypeRealmIssue` - able to issue new coins

docs/reference/standard-library/std/banker.md

@@ -28,7 +28,7 @@ Returns `Banker` of the specified type.
 
 #### Parameters
 - `BankerType` - type of Banker to get:
-    - `BankerTypeReadOnly` - read-only access to coin balances
+    - `BankerTypeReadonly` - read-only access to coin balances
     - `BankerTypeOrigSend` - full access to coins sent with the transaction that calls the banker
     - `BankerTypeRealmSend` - full access to coins that the realm itself owns, including the ones sent with the transaction
     - `BankerTypeRealmIssue` - able to issue new coins