[flang] Fix regression in submodule symbol checking (#69778)

The change #67361 removed
submodule name symbols from the name dictionaries of their parent
(sub)modules to prevent needless errors about name clashes, but these
symbols still need to be checked for things like excessive length.

flang/lib/Semantics/check-declarations.cpp

@@ -2395,6 +2395,10 @@ void CheckHelper::Check(const Scope &scope) {
     for (const auto &pair : scope) {
       Check(*pair.second);
     }
+    if (scope.IsSubmodule() && scope.symbol()) {
+      // Submodule names are not in their parent's scopes
+      Check(*scope.symbol());
+    }
     for (const auto &pair : scope.commonBlocks()) {
       CheckCommonBlock(*pair.second);
     }