Allow overriding installation URL

action.yml

@@ -1,6 +1,9 @@
 name: 'Install Nix'
 description: 'Installs Nix on GitHub Actions for the supported platforms: Linux and macOS.'
 author: 'Domen Kožar'
+inputs:
+  install_url:
+    description: 'Installation URL that will contain a script to install Nix'
 branding:
   color: 'blue'
   icon: 'sun'

lib/install-nix.sh

@@ -26,7 +26,7 @@ nixConf
 # Needed due to multi-user being too defensive
 export ALLOW_PREEXISTING_INSTALLATION=1
 
-sh <(curl -L https://nixos.org/nix/install) --daemon
+sh <(curl -L ${INPUT_INSTALL_URL:-https://nixos.org/nix/install}) --daemon
 
 # write nix.conf again as installation overwrites it
 nixConf