[ty] Fix namespace packages that behave like partial stubs (#19994)

In implementing partial stubs I had observed that this continue in the
namespace package code seemed erroneous since the same continue for
partial stubs didn't work. Unfortunately I wasn't confident enough to
push on that hunch. Fortunately I remembered that hunch to make this an
easy fix.

The issue with the continue is that it bails out of the current
search-path without testing any .py files. This breaks when for example
`google` and `google-stubs`/`types-google` are both in the same
site-packages dir -- failing to find a module in `types-google` has us
completely skip over `google`!

Fixes https://github.com/astral-sh/ty/issues/520

crates/ty_python_semantic/src/module_resolver/resolver.rs

@@ -723,8 +723,7 @@ fn resolve_name(db: &dyn Db, name: &ModuleName, mode: ModuleResolveMode) -> Opti
                          `{name}` but it is a namespace package, keep going."
                     );
                     // stub exists, but the module doesn't. But this is a namespace package,
-                    // keep searching the next search path for a stub package with the same name.
-                    continue;
+                    // fall through to looking for a non-stub package
                 }
             }
         }