Merge pull request #21648 from cohei/fix/preserve-xdg-config-home

bin/brew: preserve `XDG_CONFIG_HOME` through environment filter

Author: MikeMcQuaid

bin/brew

@@ -152,6 +152,9 @@ export_homebrew_env_file "${HOMEBREW_PREFIX}/etc/homebrew/brew.env"
 if [[ -n "${XDG_CONFIG_HOME-}" ]]
 then
   HOMEBREW_USER_CONFIG_HOME="${XDG_CONFIG_HOME}/homebrew"
+elif [[ -n "${HOMEBREW_XDG_CONFIG_HOME-}" ]]
+then
+  HOMEBREW_USER_CONFIG_HOME="${HOMEBREW_XDG_CONFIG_HOME}/homebrew"
 else
   HOMEBREW_USER_CONFIG_HOME="${HOME}/.homebrew"
 fi
@@ -213,6 +216,7 @@ USED_BY_HOMEBREW_VARS=(
   VSCODE_IPC_HOOK_CLI
   WSL_DISTRO_NAME
   XDG_CACHE_HOME
+  XDG_CONFIG_HOME
   XDG_DATA_DIRS
   XDG_RUNTIME_DIR
   ZDOTDIR