ty_python_semantic: report all union diagnostic

This makes one very simple change: we report all call binding
errors from each union variant.

This does result in duplicate-seeming diagnostics. For example,
when two union variants are invalid for the same reason.

crates/ty_python_semantic/src/types/call/bind.rs

@@ -199,11 +199,8 @@ impl<'db> Bindings<'db> {
             }
         }
 
-        // TODO: We currently only report errors for the first union element. Ideally, we'd report
-        // an error saying that the union type can't be called, followed by subdiagnostics
-        // explaining why.
-        if let Some(first) = self.into_iter().find(|b| b.as_result().is_err()) {
-            first.report_diagnostics(context, node);
+        for binding in self {
+            binding.report_diagnostics(context, node);
         }
     }