Add the random-walk and spirograph challenges to the command line

turtle-challenges random-walk and turtle-challenges spirograph, the latter with
--gap for the degrees between two circles.

Task: MIL-004#4

src/turtle_challenges/constants.py

@@ -92,9 +92,17 @@ CHALLENGE_DASHED_LINE = "dashed-line"
 ## Command line name of challenge 3.
 CHALLENGE_SHAPES = "shapes"
 
+## Command line name of challenge 4.
+CHALLENGE_RANDOM_WALK = "random-walk"
+
+## Command line name of challenge 5.
+CHALLENGE_SPIROGRAPH = "spirograph"
+
 ## Names of the challenges on the command line, in the order of the course.
 CHALLENGE_NAMES: tuple[str, ...] = (
     CHALLENGE_SQUARE,
     CHALLENGE_DASHED_LINE,
     CHALLENGE_SHAPES,
+    CHALLENGE_RANDOM_WALK,
+    CHALLENGE_SPIROGRAPH,
 )