brew should overwrite existing python links (#36192)

Summary:
Pull Request resolved: #36192

Builds are failing on CI because brew bails out when it tries installing Python 3.1. The image already has an existing version of Python 3, which we should overwrite.

{F876436464}

This seems to be a known issue [1] with Brew. In this case it seems safe to overwrite.

Changelog:
[General][Changed] - Brew overwrites system Python 3.

[1] actions/setup-python#577 (comment)

Reviewed By: cipolleschi

Differential Revision: D43391941

fbshipit-source-id: 9b0cb234eeb0b7473b17b5ebfa6ed12c6448760f

.circleci/config.yml

@@ -593,6 +593,11 @@ jobs:
       - run:
           name: "Brew: Tap wix/brew"
           command: brew tap wix/brew
+      - run:
+          # Python 3.10 already exists in the environment, this is a workaround for:
+          # https://github.com/actions/setup-python/issues/577
+          name: "Unlink environment's Python 3.10"
+          command: brew unlink python@3.10
       - brew_install:
           package: applesimutils watchman