Stabilize use of brew

Use a specific release instead of HEAD.

.gitlab-ci.yml

@@ -94,6 +94,8 @@ build-aarch64-darwin:
     TARBALL_ARCHIVE_SUFFIX: aarch64-darwin
     TARBALL_EXT: tar.xz
     ADD_CABAL_ARGS: ""
+    # Update periodically.
+    BREW_VERSION: 4.0.5
   artifacts:
     expire_in: 2 week
     paths:

.gitlab/brew.sh

@@ -1,10 +1,17 @@
 #!/usr/bin/env bash
 
-set -Eeuxo pipefail
+set -Eeuo pipefail
 
 # Install brew locally in the project dir. Packages will also be installed here.
-[ -e "$CI_PROJECT_DIR/.brew" ] || git clone --depth=1 https://github.com/Homebrew/brew $CI_PROJECT_DIR/.brew
-export PATH="$CI_PROJECT_DIR/.brew/bin:$CI_PROJECT_DIR/.brew/sbin:$PATH"
+# FIXME: Use brew in supported way. See
+# https://docs.brew.sh/Installation#untar-anywhere-unsupported
+brew_dir="${CI_PROJECT_DIR}/.brew"
+# Temporarily? ensure there's no caching accidentally happening.
+rm -fr "${brew_dir}"
+mkdir -p "${brew_dir}"
+curl -L "https://github.com/Homebrew/brew/archive/refs/tags/${BREW_VERSION}.tar.gz" | tar xz --strip 1 -C "${brew_dir}"
+
+export PATH="${brew_dir}/bin:${brew_dir}/sbin:$PATH"
 
 # make sure to not pollute the machine with temp files etc
 mkdir -p $CI_PROJECT_DIR/.brew_cache