test: add test case for setcap in Dockerfile

This is a followup of #1994. This test runs a Dockerfile where setcap is
executed. Without the fix in #1994, the last command won't generate any
diff and thus is discarded by kaniko and thus should fail this test.

integration/dockerfiles-with-context/issue-1851/Dockerfile

@@ -0,0 +1,17 @@
+# Copyright 2022 Google, Inc. All rights reserved.
+#
+# 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 wildwildangel/setcap-static:sha-a5c7425
+ADD test-file /usr/bin/test-file
+RUN ["/setcap-static", "cap_net_bind_service=+ep", "/usr/bin/test-file"]