Show a warning for the case where coverage for eval is unavailable

... instead of raising an exception

Author: mame

lib/simplecov/configuration.rb

@@ -457,7 +457,7 @@ def enable_coverage_for_eval
       if coverage_for_eval_supported?
         @coverage_for_eval_enabled = true
       else
-        raise "Coverage for eval is not available! Use Ruby 3.2.0 or later"
+        warn "Coverage for eval is not available; Use Ruby 3.2.0 or later"
       end
     end