C++20 fixes

Fix compilation with gcc13 / c++20 , ROOT 6.28.04 (LCG dev4), fmtlib 10.0.0

• use fmt::runtime where needed (with a hack to still work with fmtlib < 8)
• avoid implicit capture of this in lambdas via [=]
• fix comparison between Gaudi::Property<std::string> and const char*
• hide std::source_location to cling

Closes #266 (closed)

GaudiKernel/include/Gaudi/Accumulators/HistogramArray.h

@@ -27,7 +27,7 @@ namespace Gaudi::Accumulators {
     struct FormatHistDefault {
       std::string_view text;
       FormatHistDefault( std::string_view t ) : text{ t } {}
-      auto operator()( size_t n ) { return fmt::format( text, n ); }
+      auto operator()( size_t n ) { return fmt::format( fmt::runtime( text ), n ); }
     };
 
     /**