Bump to rules_apple v0.15.0

Should fix some BuildKite failures.

PiperOrigin-RevId: 245328655
diff --git a/WORKSPACE b/WORKSPACE
index d47016e..7988c3d 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 git_repository(
     name = "build_bazel_rules_apple",
     remote = "https://github.com/bazelbuild/rules_apple.git",
-    tag = "0.14.0",
+    tag = "0.15.0",
 )
 
 load(