[exec.schedule.from] Fix placement of declaration of "check-types"

A misapplication of P3557R3.

Author: tkoeppe

source/exec.tex

@@ -3386,10 +3386,10 @@
     static constexpr auto @\exposid{get-attrs}@ = @\seebelow@;
     static constexpr auto @\exposid{get-state}@ = @\seebelow@;
     static constexpr auto @\exposid{complete}@ = @\seebelow@;
-  };
 
-  template<class Sndr, class... Env>
-    static consteval void @\exposid{check-types}@();
+    template<class Sndr, class... Env>
+      static consteval void @\exposid{check-types}@();
+  };
 }
 \end{codeblock}