Ignore tags in universal resolution (#4174)

## Summary

If a package lacks a source distribution, and we can't find a compatible
wheel for the current platform, we need to just _assume_ that the
package will have a valid wheel on all platforms on which it's
requested; if not, we raise an error at install time.

It's possible that we can be smarter about this over time. For example,
if the package was requested _only_ for macOS, we could verify that
there's at least one macOS-compatible wheel. See the linked issue for
more details.

Closes https://github.com/astral-sh/uv/issues/4139.

crates/uv-dispatch/src/lib.rs

@@ -158,7 +158,7 @@ impl<'a> BuildContext for BuildDispatch<'a> {
             self.options,
             &python_requirement,
             Some(markers),
-            tags,
+            Some(tags),
             self.flat_index,
             self.index,
             &HashStrategy::None,