Fix minor docker build warning (ansible#15362)

Fix docker build warning

Fix
```
WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 8)
```

tools/ansible/roles/dockerfile/templates/Dockerfile.j2

@@ -5,7 +5,7 @@
 ###
 
 # Build container
-FROM quay.io/centos/centos:stream9 as builder
+FROM quay.io/centos/centos:stream9 AS builder
 
 ENV LANG en_US.UTF-8
 ENV LANGUAGE en_US:en