CMake: pro2cmake: Do not mis-report used values as ignored

Do not mis-report "PLUGIN_TYPE", "PLUGIN_CLASS_NAME", "CLASS_NAME"
and "MODULE_PLUGIN_TYPES" as ignored.

The script evaluates these.

Change-Id: I26546a7eff61a20afe68168a865fe3ac99f66319
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>

util/cmake/pro2cmake.py

@@ -1920,6 +1920,10 @@ def write_ignored_keys(scope: Scope, indent: str) -> str:
             "QT_SOURCE_TREE",
             "QT_BUILD_TREE",
             "TRACEPOINT_PROVIDER",
+            "PLUGIN_TYPE",
+            "PLUGIN_CLASS_NAME",
+            "CLASS_NAME",
+            "MODULE_PLUGIN_TYPES",
         }:
             # All these keys are actually reported already
             continue