home-environment: use explicit PATH in activation

In the activation script we expect to use the tools provided by GNU
Core Utilities and GNU Bash. This commit therefore explicitly add
these first in the `PATH` environment variable.

modules/home-environment.nix

@@ -375,6 +375,9 @@ in
           set -eu
           set -o pipefail
 
+          # We assume coreutils command and Bash.
+          export PATH="${pkgs.coreutils}/bin:${pkgs.bash}/bin/bash:$PATH"
+
           . ${./lib-bash/color-echo.sh}
 
           ${builtins.readFile ./lib-bash/activation-init.sh}