Portal docs: fix singular pronoun agreement in control-flow page (#1528)

* Initial plan

* fix: correct pronoun agreement in portal docs sentence

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

Author: Copilot

src/routes/(0)concepts/(1)control-flow/(4)portal.mdx

@@ -19,7 +19,7 @@ description: >-
 ---
 
 When an element requires rendering outside of the usual document flow, challenges related to stacking contents and z-index can interfere with the desired intention or look of an application.
-[`<Portal>`](/reference/components/portal) helps with this by putting elements in a different place in the document, bringing an element into the document flow so they can render as expected.
+[`<Portal>`](/reference/components/portal) helps with this by putting elements in a different place in the document, bringing an element into the document flow so it can render as expected.
 
 ```jsx
 import { Portal } from "solid-js/web";