Update expressions.md

[OutOfScopeia]

This PR closes #

The changes in this PR are as follows:

• doc - grammar/typos fix only

I have read the contributing guidelines and have completed the following:

• [x] Tested my code end-to-end against a live Azure subscription.
• [x] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] Updated the release notes with a new entry for this PR.
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