fix: restore @ts-expect-error for CacheProvider type mismatch (#30171)

* fix: restore @ts-expect-error for CacheProvider type mismatch

PR #30140 removed these comments assuming they were stale now that
the repo is on TypeScript 5. The comments were about the compiler
version, but the actual incompatibility is between react-inlinesvg/provider's
CacheProvider (typed to return a bare ReactNode) and this repo's pinned
@types/react@18.0.26, which requires JSX components to return Element | null.
ReactNode includes undefined, so the JSX usage fails type-checking.

Verified yarn build completes successfully with this restored.

Fixes #30170

* docs: explain the actual @ts-expect-error compatibility condition

Per @coderabbitai review on #30171: the old wording ("remove when
upgrading typescript to v5") was itself stale/misleading, since the
incompatibility is with the pinned @types/react version, not the
TypeScript compiler version. Documents the real condition instead.

apps/web/app/providers.tsx

@@ -27,6 +27,7 @@ export function Providers({ isEmbed, children, country }: ProvidersProps) {
         <TrpcProvider>
           <ToastProvider position="bottom-center">
             {!isEmbed && !isBookingPage && <NotificationSoundHandler />}
+            {/* @ts-expect-error react-inlinesvg/provider is incompatible with @types/react@18.0.26. Remove when these types are compatible. */}
             <CacheProvider>
               <WebPushProvider>{children}</WebPushProvider>
             </CacheProvider>

apps/web/pages/_app.tsx

@@ -17,6 +17,7 @@ function MyApp(props: AppProps) {
   return (
     <SessionProvider session={pageProps.session ?? undefined}>
       <WebPushProvider>
+        {/* @ts-expect-error react-inlinesvg/provider is incompatible with @types/react@18.0.26. Remove when these types are compatible. */}
         <CacheProvider>
           {Component.PageWrapper ? <Component.PageWrapper {...props} /> : <Component {...pageProps} />}
         </CacheProvider>