[CI] Add missing field for pull request BQ table (#822)

#797 introduced a new field for pull request data, `pull_request_state`.
However, this field was mistakenly left out of the BigQuery schema which
causes daily workflows to fail when trying to upload data.

Author: jriv01

premerge/bigquery_schema/llvm_pull_requests_table_schema.json

@@ -29,6 +29,12 @@
     "mode": "NULLABLE",
     "description": "Number of the pull request."
   },
+  {
+    "name": "pull_request_state",
+    "type": "STRING",
+    "mode": "NULLABLE",
+    "description": "The state of this pull request (OPEN, MERGED, etc)"
+  },
   {
     "name": "associated_commit",
     "type": "STRING",