Update macOS install script (#21854)

util/install/macos.sh

@@ -19,8 +19,13 @@ _qmk_install() {
     # https://github.com/qmk/homebrew-qmk
     brew install qmk/qmk/qmk
 
+    # Conflicts with new toolchain formulae
+    brew uninstall --ignore-dependencies arm-gcc-bin@8 >/dev/null 2>&1
+
+    # Keg-only, so need to be manually linked
     brew link --force avr-gcc@8
-    brew link --force arm-gcc-bin@8
+    brew link --force arm-none-eabi-binutils
+    brew link --force arm-none-eabi-gcc@8
 
     python3 -m pip install -r $QMK_FIRMWARE_DIR/requirements.txt
 }