Set compatible_with=appengine on GAE targets

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=128475519

java/google/registry/backup/BUILD

@@ -8,6 +8,7 @@ licenses(["notice"])  # Apache 2.0
 java_library(
     name = "backup",
     srcs = glob(["*.java"]),
+    compatible_with = ["//buildenv/target:appengine"],
     deps = [
         "//java/com/google/common/annotations",
         "//java/com/google/common/base",