validate yaml for extraneous fields in pkg build

Signed-off-by: Avi Deitcher <avi@deitcher.net>

test/cases/000_build/090_validate_build_yaml/Dockerfile

@@ -0,0 +1,2 @@
+FROM alpine:3.22
+

test/cases/000_build/090_validate_build_yaml/build.yml

@@ -0,0 +1,7 @@
+image: build-args-test
+network: true
+arches:
+    - amd64
+    - arm64
+# should error out on this unknown field
+unknownField: "abc"

test/cases/000_build/090_validate_build_yaml/test.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+# SUMMARY: Check that the build-args are correctly passed to Dockerfiles
+# LABELS:
+# REPEAT:
+
+set -ex
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+# Test code goes here
+RESULT=$(linuxkit pkg build --force . 2>&1 || echo FAILED)
+if [ "${RESULT}" != "FAILED" ]; then
+    echo "Build should have failed with invalid yaml, instead was ${RESULT}"
+fi
+echo "Summary: correctly detected invalid yaml"
+
+exit 0