fix: add GeneratedCompletion to installer T.cast union types

The cask installer's install_phase and uninstall_phase methods use
T.cast with an explicit union of artifact types. GeneratedCompletion
was missing, causing a runtime T.cast error during cask installation.

Author: mvanhorn

Library/Homebrew/cask/installer.rb

@@ -333,6 +333,7 @@ def install_artifacts(predecessor: nil)
           artifact,
           T.any(
             Artifact::AbstractFlightBlock,
+            Artifact::GeneratedCompletion,
             Artifact::Installer,
             Artifact::KeyboardLayout,
             Artifact::Mdimporter,
@@ -600,6 +601,7 @@ def uninstall_artifacts(clear: false, successor: nil)
             artifact,
             T.any(
               Artifact::AbstractFlightBlock,
+              Artifact::GeneratedCompletion,
               Artifact::KeyboardLayout,
               Artifact::Moved,
               Artifact::Qlplugin,