Update the comment in SpawnExec since we've changed the behaviour: on remote cache hits, rather than leaving the runner empty we set it to "remote cache hit".

RELNOTES: None
PiperOrigin-RevId: 210903867
diff --git a/src/main/protobuf/spawn.proto b/src/main/protobuf/spawn.proto
index b6c6ec3..529819f 100644
--- a/src/main/protobuf/spawn.proto
+++ b/src/main/protobuf/spawn.proto
@@ -99,9 +99,13 @@
   // The outputs generated by the execution.
   repeated File actual_outputs = 11;
 
-  // If the Spawn was actually executed, rather than a remote cache hit,
+  // If the Spawn was actually executed, rather than a cache hit,
   // this will be the name of the runner executing the spawn, e.g. remote or
-  // linux-sandbox. Note this is not the same as the "strategy" string -- even
+  // linux-sandbox. If it was a remote cache hit, the runner will be
+  // "remote cache hit". If it was a local cache hit, the action will not be
+  // inluded in the log in the first place.
+  //
+  // Note this is not the same as the "strategy" string -- even
   // though the action strategy may be remote, a particular action may still
   // fall back to local execution due to a variety of reasons. This field
   // indicates what really happened for the particular Spawn+execution.