ci: Disable nix cache on self-hosted runners (#786)

In an attempt to speed up Nutanix e2e tests.

Author: jimmidyson

.github/workflows/e2e.yml

@@ -50,7 +50,7 @@ jobs:
       - name: Install devbox
         uses: jetify-com/[email protected]
         with:
-          enable-cache: "true"
+          enable-cache: ${{ inputs.runs-on != 'self-hosted-ncn-dind' }}
           skip-nix-installation: ${{ inputs.runs-on == 'self-hosted-ncn-dind' }}
 
       - name: Go cache