fix(people): replace placeholder portrait alt text

Author: rushdarshan

src/content/people/en/kenneth-lim.yaml

@@ -2,7 +2,7 @@ name: Kenneth Lim
 url: https://limzykenneth.com/
 category: mentor
 image: ../images/kenneth-lim.jpeg
-imageAlt: WRITE ALT TEXT HERE
+imageAlt: Portrait of Kenneth Lim
 role: p5.js Mentor, 2023-present
 order: 4
 blurb: >

src/content/people/en/stalgia-grigg.yaml

@@ -1,7 +1,7 @@
 name: Stalgia Grigg
 category: alumni
 image: ../images/stalgia-grigg.png
-imageAlt: WRITE ALT TEXT HERE
+imageAlt: Portrait of Stalgia Grigg
 url: https://stalgiagrigg.name/
 role: p5.js Fellow 2019
 order: 9