ci(macos): untap untrusted aws/tap on macOS

Problem: The 3rd-party default homebrew tap `aws/tap` is untrusted,
which now triggers a warning in our macOS workflows.

Solution: "Untap" (disable) the tap (which we don't use).

.github/scripts/install_deps.sh

@@ -50,6 +50,7 @@ if [[ $OS == Linux ]]; then
   fi
 elif [[ $OS == Darwin ]]; then
   if [[ -n $TEST ]]; then
+    brew untap aws/tap
     brew install cpanminus fish fswatch
 
     npm install -g neovim