Fix wxPropertySheetDialog::SetInnerSize() ABI breakage in 3.0.3

Add back the old method name, replacing it with SetInnerSizer() in
6b335c8ca4 wasn't ABI (nor even API) compatible.

Still keep SetInnerSizer() and do _not_ add it to version-script.in to avoid
breaking compatibility with 3.0.3 now.

Closes #17861.

include/wx/generic/propdlg.h

@@ -109,7 +109,12 @@ public:
     virtual wxWindow* GetContentWindow() const;
 
     // Set and get the inner sizer
+
+    // Keep old version with a typo in it for ABI compatibility.
+    void SetInnerSize(wxSizer* sizer) { m_innerSizer = sizer; }
+#if wxABI_VERSION >= 30003
     void SetInnerSizer(wxSizer* sizer) { m_innerSizer = sizer; }
+#endif
     wxSizer* GetInnerSizer() const { return m_innerSizer ; }
 
     // Set and get the book style