Update Linux build agents

.github/workflows/linux.yml

@@ -23,13 +23,13 @@ jobs:
         include:
         - vscode_arch: x64
           npm_arch: x64
-          image: vscodium/vscodium-linux-build-agent:x64
+          image: vscodium/vscodium-linux-build-agent:bionic-x64
         - vscode_arch: arm64
           npm_arch: arm64
-          image: vscodium/vscodium-linux-build-agent:buster-arm64
+          image: vscodium/vscodium-linux-build-agent:stretch-arm64
         - vscode_arch: armhf
           npm_arch: armv7l
-          image: vscodium/vscodium-linux-build-agent:buster-armhf
+          image: vscodium/vscodium-linux-build-agent:stretch-armhf
 
     steps:
       - uses: actions/checkout@v2