BPY/UI: Rename pie menu emboss type

Renames `'RADIAL_MENU'` to `'PIE_MENU'`, to more clearly describe what
it relates to. Internally this was already done with e425faf696.

This is a 5.0 compatibility breaking change. But I couldn't find any
usages of it in bundled scripts.

Pull Request: https://projects.blender.org/blender/blender/pulls/146651

source/blender/makesrna/intern/rna_ui.cc

@@ -1692,11 +1692,7 @@ static void rna_def_ui_layout(BlenderRNA *brna)
        0,
        "Pull-down Menu",
        "Draw pull-down menu style"},
-      {int(blender::ui::EmbossType::PieMenu),
-       "RADIAL_MENU",
-       0,
-       "Pie Menu",
-       "Draw radial menu style"},
+      {int(blender::ui::EmbossType::PieMenu), "PIE_MENU", 0, "Pie Menu", "Draw radial menu style"},
       {int(blender::ui::EmbossType::NoneOrStatus),
        "NONE_OR_STATUS",
        0,