maint: update OS for Linux arm64

We think only x64 should stay on 20.04 for now so it can work on old Ubuntu/Debian installs

.github/workflows/release.yml

@@ -24,7 +24,7 @@ jobs:
           - target: x86_64-unknown-linux-musl
             os: ubuntu-latest
           - target: aarch64-unknown-linux-gnu
-            os: ubuntu-20.04
+            os: ubuntu-latest
           - target: aarch64-unknown-linux-musl
             os: ubuntu-latest
           - target: x86_64-pc-windows-msvc