docs: replace \| with | inside a backtick code block in a table

Created by: ijt

Fixes #3869 (closed)

This change depends on https://github.com/sourcegraph/docsite/pull/18 being deployed.

Test plan: Check https://docs.sourcegraph.com/@doc-fix/user/search/queries and see if the first row of the table looks reasonable.

Before:

After: