Fix suffix see compiler-explorer/infra#1556

Author: mattgodbolt

.github/workflows/build.yml

@@ -16,7 +16,7 @@ jobs:
           # otherwise we somehow need to apply 947f9692440836dcb8d88b74b69dd379d85974ce to get the sanitizer
           # to build.
         - image: 16.04
-          suffix: -16.4
+          suffix: -16.04
           # Ancient Clang builds (2.6-4.0) assume 16.04 environment. 
     steps:
     - name: Docker Setup Buildx