Build on Ubuntu 20.04 for older glibc

.github/workflows/full_build.yml

@@ -26,22 +26,22 @@ jobs:
             vs-code-target: win32-arm64
             features: --no-default-features -F remote-packages,native-tls
 
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             rust-target: x86_64-unknown-linux-gnu
             vs-code-target: linux-x64
             features:
 
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             rust-target: aarch64-unknown-linux-gnu
             vs-code-target: linux-arm64
             features:
 
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             rust-target: x86_64-unknown-linux-musl
             vs-code-target: alpine-x64
             features:
 
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             rust-target: arm-unknown-linux-gnueabihf
             vs-code-target: linux-armhf
             features: