project: make a list from filtered project iterator

`filter` is not indexable, but the parallel update implementation requires that
it is.

Before this patch, `west update -j2 PROJECT_NAME` failed with:
TypeError: 'filter' object is not subscriptable

Signed-off-by: Michael Zimmermann <sigmaepsilon92@gmail.com>

src/west/app/project.py

@@ -1038,9 +1038,9 @@ class Update(_ProjectCommand):
         else:
             projects = self._projects(self.args.projects)
 
-        projects = filter(
+        projects = list(filter(
             lambda p: not isinstance(
-                p, ManifestProject), projects)
+                p, ManifestProject), projects))
 
         (failed, updated) = self.update_project_list(projects)