Add missing load statements for proto_library

This makes Bazel compatible with
`--incompatible_load_proto_rules_from_bzl`, which was presumably broken by
https://github.com/bazelbuild/bazel/commit/65970e5e19d0e30a03fa0cb3dcf660a4a141ab25.

This change was generated by `buildifier --lint=fix
--warnings=native-proto -r src/main src/test/java`.

Closes #10883.

PiperOrigin-RevId: 298904410
diff --git a/src/main/java/com/google/devtools/build/skyframe/BUILD b/src/main/java/com/google/devtools/build/skyframe/BUILD
index 86dcbca..cec51f5 100644
--- a/src/main/java/com/google/devtools/build/skyframe/BUILD
+++ b/src/main/java/com/google/devtools/build/skyframe/BUILD
@@ -1,4 +1,5 @@
 load("@rules_java//java:defs.bzl", "java_library")
+load("@rules_proto//proto:defs.bzl", "proto_library")
 load("//tools/build_rules:utilities.bzl", "java_library_srcs")
 
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