Fixed usage of fmt::format and fmt::print for C++20 (#323)

With C++20 `fmt::print(s)` expects a compile time format string and
otherwise fails complaining about consteval. To get runtime formatting
use `fmt::print(fmt::runtime(s))`

src/defs.cpp

@@ -7,7 +7,7 @@
 namespace aare {
 
 void assert_failed(const std::string &msg) {
-    fmt::print(msg);
+    fmt::print("{}", msg);
     exit(1);
 }