chore: fix compilation (open-telemetry#705)

Author: dyladan

packages/opentelemetry-plugin-postgres/opentelemetry-plugin-pg-pool/test/pg-pool.test.ts

@@ -186,6 +186,12 @@ describe('pg-pool@2.x', () => {
           if (err) {
             return done(err);
           }
+          if (!release) {
+            throw new Error('Did not receive release function');
+          }
+          if (!client) {
+            throw new Error('No client received');
+          }
           release();
           assert.ok(client);
           runCallbackTest(parentSpan, pgPoolattributes, events, okStatus, 1, 0);