Fix bad field type in ScriptRequestIncident.

BUG=none
R=noelutz@google.com

Review URL: https://codereview.chromium.org/1031963002

Cr-Commit-Position: refs/heads/master@{#322515}

chrome/common/safe_browsing/csd.proto

@@ -383,7 +383,7 @@ message ClientIncidentReport {
       optional string variations_seed_signature = 1;
     }
     message ScriptRequestIncident {
-      optional string script_digest = 1;
+      optional bytes script_digest = 1;
       optional string inclusion_origin = 2;
     }
     optional int64 incident_time_msec = 1;