Type cast img dom search

Co-authored-by: Alexander Brandon Coles <a.coles@openproject.com>

Author: akabiru

app/components/primer/open_project/avatar_fallback.ts

@@ -10,7 +10,7 @@ export class AvatarFallbackElement extends HTMLElement {
     // keeps its default gray fill defined in the source and no color override is applied.
     if (!this.uniqueId || !this.altText) return
 
-    const img = this.querySelector('img[src^="data:image/svg+xml"]')
+    const img = this.querySelector<HTMLImageElement>('img[src^="data:image/svg+xml"]')
     if (!img) return
 
     // Generate consistent color based on uniqueId and altText (hash must match OP Core)