Fix case sensitivity in validator

Author: T90REAL

src/marshmallow/validate.py

@@ -187,7 +187,7 @@ def __init__(
         self.relative = relative
         self.absolute = absolute
         self.error: str = error or self.default_message
-        self.schemes = schemes or self.default_schemes
+        self.schemes = {s.lower() for s in schemes} if schemes else self.default_schemes
         self.require_tld = require_tld
 
     def _repr_args(self) -> str:

tests/test_validate.py

@@ -205,6 +205,14 @@ def test_url_custom_scheme():
     assert validator(url) == url
 
 
+def test_url_custom_scheme_case_insensitive():
+    validator = validate.URL(schemes={"HTTP"})
+    assert validator("http://example.com") == "http://example.com"
+
+    validator = validate.URL(schemes={"HtTp"})
+    assert validator("hTtP://example.com") == "hTtP://example.com"
+
+
 @pytest.mark.parametrize(
     "valid_url",
     (