fix(docs): wrong GetOrigCaller usage reference (gnolang#2659)

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## Description

Small fix for the docs.

<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
- [x] 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/reference/stdlibs/std/chain.md

@@ -85,7 +85,7 @@ Returns the original signer of the transaction.
 
 #### Usage
 ```go
-caller := std.GetOrigSend()
+caller := std.GetOrigCaller()
 ```
 ---