add GitHub Action arm64 runners for Ubuntu

https://github.blog/changelog/2025-01-16-linux-arm64-hosted-runners-now-available-for-free-in-public-repositories-public-preview/

Author: peterbecich

.github/workflows/build.yml

@@ -14,6 +14,7 @@ jobs:
       matrix:
         include:
           - os: ubuntu-latest
+          - os: ubuntu-24.04-arm
           - os: macOS-latest
           - os: windows-latest
     steps:

.github/workflows/nix-flake.yml

@@ -14,6 +14,7 @@ jobs:
       matrix:
         include:
           - os: ubuntu-latest
+          - os: ubuntu-24.04-arm
           - os: macOS-latest
     steps:
       - uses: actions/checkout@v4