Avoid 403 error hint for PyTorch URLs (#9750)

## Summary

Closes #9746.

crates/uv-resolver/src/pubgrub/report.rs

@@ -793,6 +793,12 @@ impl PubGrubReportFormatter<'_> {
                 });
             }
             if index_capabilities.forbidden(&index.url) {
+                // If the index is a PyTorch index (e.g., `https://download.pytorch.org/whl/cu118`),
+                // avoid noting the lack of credentials. PyTorch returns a 403 (Forbidden) status
+                // code for any package that does not exist.
+                if index.url.url().host_str() == Some("download.pytorch.org") {
+                    continue;
+                }
                 hints.insert(PubGrubHint::ForbiddenIndex {
                     index: index.url.clone(),
                 });

crates/uv/tests/it/lock.rs

@@ -14017,8 +14017,6 @@ fn lock_default_index() -> Result<()> {
     ----- stderr -----
       × No solution found when resolving dependencies:
       ╰─▶ Because iniconfig was not found in the package registry and your project depends on iniconfig, we can conclude that your project's requirements are unsatisfiable.
-
-          hint: An index URL (https://download.pytorch.org/whl/cu121) could not be queried due to a lack of valid authentication credentials (403 Forbidden).
     "###);
 
     let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();

crates/uv/tests/it/pip_compile.rs

@@ -6703,8 +6703,6 @@ fn index_url_in_requirements() -> Result<()> {
     ----- stderr -----
       × No solution found when resolving dependencies:
       ╰─▶ Because anyio was not found in the package registry and you require anyio<4, we can conclude that your requirements are unsatisfiable.
-
-          hint: An index URL (https://download.pytorch.org/whl) could not be queried due to a lack of valid authentication credentials (403 Forbidden).
     "###
     );