[CS] Avoid setting hadError for diagnoseUnhandledThrowsInAsyncContext

We can still apply the solution even if we emit an error here. No
test since it's already covered in the test suite once the next commit
is applied.

Author: hamishknight

lib/Sema/CSSyntacticElement.cpp

@@ -1977,8 +1977,8 @@ class SyntacticElementSolutionApplication
 
     // Check to see if the sequence expr is throwing (in async context),
     // if so require the stmt to have a `try`.
-    hadError |= diagnoseUnhandledThrowsInAsyncContext(
-        context.getAsDeclContext(), forEachStmt);
+    diagnoseUnhandledThrowsInAsyncContext(context.getAsDeclContext(),
+                                          forEachStmt);
 
     return forEachStmt;
   }