Fix typo in schemas for messaging attribute changes

[JamieDanielson]

Changes

While reviewing recent semantic convention changes, I noticed these typos for messaging changes.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[lmolkova]

Thank you!

[lmolkova]

it seems we should not update old schemas -

semantic-conventions/CONTRIBUTING.md

Lines 140 to 141 in c5093dd

	> DO NOT add your changes to files inside the `schemas` folder. Always add your
	> changes to the `schema-next.yaml` file.

I'd like to stop producing/updating these files manually - #1596.

Curious what brought your attention to these files, @JamieDanielson ? Do you happen to use them in any way?