d/rules: use variables instead of hardcoded ruby version in dh_gencontrol

Author: lucaskanashiro

debian/rules

@@ -159,6 +159,6 @@ override_dh_install-arch:
 	dh_install
 
 override_dh_gencontrol:
-	./debian/genprovides $(CURDIR)/debian/libruby3.0/usr/lib/ruby/gems/3.0.0/specifications/default/ \
-		>> debian/libruby3.0.substvars
+	./debian/genprovides $(CURDIR)/debian/libruby$(RUBY_VERSION)/usr/lib/ruby/gems/$(RUBY_API_VERSION)/specifications/default/ \
+		>> debian/libruby$(RUBY_VERSION).substvars
 	dh_gencontrol