docs: fix XCM docs for AlwaysV4 and AlwaysV5 (#8862)

✄
-----------------------------------------------------------------------------

Thank you for your Pull Request! 🙏 Please make sure it follows the
contribution guidelines outlined in [this

document](https://github.com/paritytech/polkadot-sdk/blob/master/docs/contributor/CONTRIBUTING.md)
and fill out the
sections below. Once you're ready to submit your PR for review, please
delete this section and leave only the text under
the "Description" heading.

# Description

Fix docstrings for `AlwaysV4` and `AlwaysV5` in XCM code, both of which
wrongly stated V3

## Integration

Only docs are changed.

## Review Notes

None


# Checklist

* [x] My PR includes a detailed description as outlined in the
"Description" and its two subsections above.
* [x] My PR follows the [labeling requirements](

https://github.com/paritytech/polkadot-sdk/blob/master/docs/contributor/CONTRIBUTING.md#Process
) of this project (at minimum one label for `T` required)
* External contributors: ask maintainers to put the right label on your
PR.
* [x] I have made corresponding changes to the documentation (if
applicable)
* [x] (N/A) I have added tests that prove my fix is effective or that my
feature works (if applicable)

You can remove the "Checklist" section once all have been checked. Thank
you for your contribution!

✄
-----------------------------------------------------------------------------

Author: andrew-ifrita

polkadot/xcm/src/lib.rs

@@ -479,7 +479,7 @@ impl GetVersion for AlwaysV3 {
 	}
 }
 
-/// `WrapVersion` implementation which attempts to always convert the XCM to version 3 before
+/// `WrapVersion` implementation which attempts to always convert the XCM to version 4 before
 /// wrapping it.
 pub struct AlwaysV4;
 impl WrapVersion for AlwaysV4 {
@@ -496,7 +496,7 @@ impl GetVersion for AlwaysV4 {
 	}
 }
 
-/// `WrapVersion` implementation which attempts to always convert the XCM to version 3 before
+/// `WrapVersion` implementation which attempts to always convert the XCM to version 5 before
 /// wrapping it.
 pub struct AlwaysV5;
 impl WrapVersion for AlwaysV5 {