[8.x] Change model_id column on runway_uris table to a string (#656)

Author: duncanmcclean

database/migrations/2021_05_04_162552_create_runway_uris_table.php

@@ -17,7 +17,7 @@ public function up()
             $table->id();
             $table->string('uri');
             $table->string('model_type');
-            $table->bigInteger('model_id');
+            $table->string('model_id', 36);
             $table->timestamps();
         });
     }