docs: add Event.exceptions.value to PII fields (#16130)

Author: colinkawai

src/data/relay_event_pii.json

@@ -43,6 +43,10 @@
     "path": "Event.exceptions.stacktrace.frames.vars",
     "additional_properties": false
   },
+  {
+    "path": "Event.exceptions.value",
+    "additional_properties": false
+  },
   {
     "path": "Event.expectct",
     "additional_properties": false