refactor(sonar): mark converting constructors explicit (cpp:S1709)

sound_source and the gl::object conversion operators stay implicit; they
are relied upon by copy-list-initialisation and GL calls.

gl/query.h

@@ -25,7 +25,7 @@ protected:
 	GLenum glenum_target(targets target) const;
 
 public:
-	query(targets target);
+	explicit query(targets target);
 	~query();
 
 	void begin();