Valgrind: Use named classes for run worker factories

Change-Id: I05009aa2fe4541e10fa56a3a095db030e18b79b5
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/valgrind/callgrindtool.h

@@ -3,10 +3,7 @@
 
 #pragma once
 
-namespace Valgrind {
-namespace Internal {
-
-class ValgrindGlobalSettings;
+namespace Valgrind::Internal {
 
 class CallgrindTool final
 {
@@ -15,5 +12,4 @@ public:
     ~CallgrindTool();
 };
 
-} // namespace Internal
-} // namespace Valgrind
+} // Valgrind::Internal