ci: Use self-hosted runner

.github/workflows/ci.yml

@@ -13,16 +13,9 @@ on:
 
 # A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
-  # This workflow contains a single job called "build"
   build:
-    # The type of runner that the job will run on
-    runs-on: ubuntu-latest
+    runs-on: x86_64-linux
 
-    # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@main
-      - uses: DeterminateSystems/magic-nix-cache-action@main
-      - name: Install omnix
-        run: nix --accept-flake-config profile install "github:juspay/omnix"
       - run: om ci

README.md

@@ -14,6 +14,6 @@ just deploy ny-ci-nixos
 
 ## Progress
 
-- [ ] NixOS CI: Running GitHub runners
+- [x] NixOS CI: Running GitHub runners
 - [x] Refactor to prepare for multiple hosts
 - [ ] macOS CI: nix-darwin