github: annotate build warnings

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

__tests__/fixtures/lint.Dockerfile

@@ -0,0 +1,28 @@
+# syntax=docker/dockerfile-upstream:master
+
+# Copyright 2024 actions-toolkit authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+frOM busybox as base
+cOpy lint.Dockerfile .
+
+from scratch
+MAINTAINER moby@example.com
+COPy --from=base \
+  /lint.Dockerfile \
+  /
+
+CMD [ "echo", "Hello, Norway!" ]
+CMD [ "echo", "Hello, Sweden!" ]
+ENTRYPOINT my-program start