Add sharding for SkyframeTests

Closes #10314.

PiperOrigin-RevId: 283331559

src/test/java/com/google/devtools/build/lib/skyframe/BUILD

diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/BUILD b/src/test/java/com/google/devtools/build/lib/skyframe/BUILD
index c2cf3e1..b380cac 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/BUILD
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/BUILD
@@ -60,7 +60,7 @@
             exclude = ["MacOSXFsEventsDiffAwarenessTest.java"],
         ),
     }),
-    flaky = 1,
+    shard_count = 20,
     tags = ["skyframe"],
     test_class = "com.google.devtools.build.lib.AllTests",
     deps = [