Fixes type collision for enum values that start with _ (underscore) (oapi-codegen#1438)

Co-authored-by: Ula <ulad@users.noreply.github.com>
Co-authored-by: Marcin Romaszewicz <mromaszewicz@users.noreply.github.com>

Author: 3 people

pkg/codegen/utils_test.go

@@ -604,6 +604,7 @@ func TestSchemaNameToTypeName(t *testing.T) {
 		"=3":           "Equal3",
 		"#Tag":         "HashTag",
 		".com":         "DotCom",
+		"_1":           "Underscore1",
 		">=":           "GreaterThanEqual",
 		"<=":           "LessThanEqual",
 		"<":            "LessThan",