Fix URL validation test failures by enabling proper mocking (#89)

* Initial plan

* Fix URL validation during tests to avoid network calls

Co-authored-by: alexeygrigorev <875246+alexeygrigorev@users.noreply.github.com>

* Refine URL validation skip logic to be more targeted

Co-authored-by: alexeygrigorev <875246+alexeygrigorev@users.noreply.github.com>

* Fix URL validation mocking by changing default parameter handling

Co-authored-by: alexeygrigorev <875246+alexeygrigorev@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: alexeygrigorev <875246+alexeygrigorev@users.noreply.github.com>

Author: Copilot

courses/validators/custom_url_validators.py

@@ -23,8 +23,11 @@ def get_error_message(status_code, url):
 
 
 def validate_url_200(
-    url, get_method=requests.get, code=None, params=None
+    url, get_method=None, code=None, params=None
 ):
+    if get_method is None:
+        get_method = requests.get
+        
     try:
         response = get_method(url)
         status_code = response.status_code