Fix 'the the' typos in comments (#9554)

src/mapgen/mapgen_valleys.cpp

@@ -390,7 +390,7 @@ int MapgenValleys::generateTerrain()
 
 		// Rivers are placed where 'river' is negative
 		if (river < 0.0f) {
-			// Use the the function -sqrt(1-x^2) which models a circle
+			// Use the function -sqrt(1-x^2) which models a circle
 			float tr = river / river_size_factor + 1.0f;
 			float depth = (river_depth_bed *
 				std::sqrt(std::fmax(0.0f, 1.0f - tr * tr)));

src/script/common/c_internal.cpp

@@ -47,7 +47,7 @@ int script_exception_wrapper(lua_State *L, lua_CFunction f)
 /*
  * Note that we can't get tracebacks for LUA_ERRMEM or LUA_ERRERR (without
  * hacking Lua internals).  For LUA_ERRMEM, this is because memory errors will
- * not execute the the error handler, and by the time lua_pcall returns the
+ * not execute the error handler, and by the time lua_pcall returns the
  * execution stack will have already been unwound.  For LUA_ERRERR, there was
  * another error while trying to generate a backtrace from a LUA_ERRRUN.  It is
  * presumed there is an error with the internal Lua state and thus not possible