Bump from ignition 5a45ee84 to af7bcce09"

Stop building ignition before the stabilization and start using 3.6
instead of 3.6-experimental.

The commit includes the stabilization of ignition 3.6:
  coreos/ignition#2202

Signed-off-by: Alice Frosi <afrosi@redhat.com>

Author: alicefr

.github/workflows/build-ignition-image.yml

@@ -3,7 +3,7 @@ name: "Build and push Ignition container image"
 env:
   NAME: "ignition"
   REGISTRY: "quay.io/trusted-execution-clusters"
-  COMMIT: "5a45ee84"
+  COMMIT: "af7bcce09"
 
 on:
   push: