Upgrade to TS7 official release (#6958)

# Description of Changes
Convert from the TS7 release candidate to the TS7 official release,
keeping TS6 around in [the compatibility mode suggested by
Microsoft](https://devblogs.microsoft.com/typescript/announcing-typescript-7-0/#running-side-by-side-with-typescript-6.0)
so ESLint and our scripts which rely on the TS API still work.

.taskfiles/frontend.yml

@@ -262,10 +262,8 @@ tasks:
 
   typecheck:_run:
     internal: true
-    env:
-      CI: '{{ .CI | default "false" }}'
     cmds:
-      - '{{ if eq .CI "true" }}npx tsc{{ else }}npx tsgo{{ end }} --noEmit --project {{.PROJECT}}'
+      - 'npx tsc --noEmit --project {{.PROJECT}}'
 
   typecheck:core:
     desc: "Typecheck core build variant"