Update brew.plugin.zsh (#6947)

add aliases for `brew pin` and `brew list --pinned`

plugins/brew/brew.plugin.zsh

@@ -1,4 +1,6 @@
+alias brewp='brew pin'
 alias brews='brew list -1'
+alias brewsp='brew list --pinned'
 alias bubo='brew update && brew outdated'
 alias bubc='brew upgrade && brew cleanup'
 alias bubu='bubo && bubc'