Force relink Python

Author: ychin

.github/workflows/ci-macvim.yaml

@@ -113,9 +113,16 @@ jobs:
         env:
           HOMEBREW_NO_AUTO_UPDATE: 1
         run: |
-          brew install python
+          brew install python3
           brew install ruby
           brew install lua
+
+          # CI sometimes have custom installed Python instead of using Homebrew. Forcefully re-
+          # link Python, and then check that we are using the Homebrew version. This avoids us
+          # using a mystery Python installation that we don't control.
+          brew unlink python3 && brew link --overwrite python3
+          readlink -f $vi_cv_path_python3 | grep "^$(brew --cellar python3)"
+
           if [[ -d /usr/local/Cellar/perl ]]; then
             # We just use system perl to reduce dependencies
             brew unlink perl