Add test case for HTTPS credentials on direct URL in `uv export` (#13808)

Related to 

- #13799 
- #13792

crates/uv/tests/it/export.rs

@@ -1142,7 +1142,7 @@ fn requirements_txt_non_project() -> Result<()> {
 
 #[cfg(feature = "git")]
 #[test]
-fn requirements_txt_git_credentials() -> Result<()> {
+fn requirements_txt_https_git_credentials() -> Result<()> {
     let context = TestContext::new("3.12");
     let token = decode_token(READ_ONLY_GITHUB_TOKEN);
 
@@ -1174,6 +1174,40 @@ fn requirements_txt_git_credentials() -> Result<()> {
     Ok(())
 }
 
+#[cfg(feature = "git")]
+#[test]
+fn requirements_txt_https_credentials() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(&formatdoc! {r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig @ https://public:heron@pypi-proxy.fly.dev/basic-auth/files/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl"]
+    "#})?;
+
+    context.lock().assert().success();
+
+    // The credentials are for a direct URL, and are included in the export
+    uv_snapshot!(context.filters(), context.export(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv export --cache-dir [CACHE_DIR]
+    iniconfig @ https://public:****@pypi-proxy.fly.dev/basic-auth/files/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl \
+        --hash=sha256:b6a85871a79d2e3b22d2d1b94ac2824226a63c6b741c88f7ae975f18b6778374
+        # via project
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    ");
+
+    Ok(())
+}
+
 #[test]
 fn requirements_txt_non_project_marker() -> Result<()> {
     let context = TestContext::new("3.12");