Potential fix for code scanning alert no. 12: Failure to use HTTPS URLs

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: bug-ops

crates/feedparser-rs-core/tests/http_integration.rs

@@ -700,7 +700,7 @@ mod http_tests {
     #[test]
     fn test_invalid_etag_returns_error() {
         let result = test_get(
-            "http://example.com/feed.xml",
+            "https://example.com/feed.xml",
             Some("\n\r"),
             None,
             None,
@@ -719,7 +719,7 @@ mod http_tests {
     #[test]
     fn test_invalid_last_modified_returns_error() {
         let result = test_get(
-            "http://example.com/feed.xml",
+            "https://example.com/feed.xml",
             None,
             Some("\n\r"),
             None,