Make a copy of the gaxOpts parameter

Don’t modify the gaxOptions parameter in place and pass it down. This change makes it so that changes to gax options downstream will not affect gaxOptions in this layer of the call stack which is desirable and which also allows the failing test to pass.

src/table.ts

@@ -894,7 +894,7 @@ Please use the format 'prezzy' or '${instance.name}/tables/prezzy'.`);
         reqOpts.rowsLimit = rowsLimit - rowsRead;
       }
 
-      options.gaxOptions = populateAttemptHeader(
+      const gaxOpts = populateAttemptHeader(
         numRequestsMade,
         options.gaxOptions
       );
@@ -903,7 +903,7 @@ Please use the format 'prezzy' or '${instance.name}/tables/prezzy'.`);
         client: 'BigtableClient',
         method: 'readRows',
         reqOpts,
-        gaxOpts: options.gaxOptions,
+        gaxOpts,
         retryOpts,
       });