Fix encore + clerk ts template

[paulwei-se]

The typescripts tutorial at https://encore.dev/templates/clerk will result to an error if followed exactly.
ERR error="Failed to resolve JWK during verification." endpoint=myAuthHandler service=auth span_id=j6k6he3h81maq trace_id=8833e0movdg4acttoo6vga3qpo

according to Clerk document: https://clerk.com/docs/references/backend/verify-token#verify-token-options
verifyToken() at auth/auth.ts:35 must set the secretKey

The following code should fix it:

    const result = await verifyToken(token, {
      secretKey: clerkSecretKey(), // add this line
      authorizedParties: AUTHORIZED_PARTIES,
    });