Incr. size dummy QACanvas to 5x5 pixels, fix bad text size w/ Deb12

Redmine: Refs #3151

Avoid crazy values in automatic computation of Pad and text sizes under Debian12 (and maybe other OSes, but at least on this one it leads to an error message)

@f.uhlig not sure if it needs to be backported to the release as only the tracking QA is affected from what I could see in the CI

core/qa/CbmQaCanvas.h

@@ -52,7 +52,9 @@ class CbmQaCanvas : public TCanvas {
   {
     /// the static variable will be initialised at the first call;
     /// deleted at the application end (c++11)
-    static CbmQaCanvas dummy("CbmQaDummyCanvas", "CbmQaDummyCanvas", 1, 1);
+    /// Note: Sizes 1x1 to 3x3 pixels lead to crazy text size and an error under Debian 12
+    /// Note: Size 4x4 lead to a pad with size 0 and not statbox  under Debian 12
+    static CbmQaCanvas dummy("CbmQaDummyCanvas", "CbmQaDummyCanvas", 5, 5);
     return dummy;
   }