fix(database): define increment in modular API (#8377)

---------
Co-authored-by: jude.kwashie <[email protected]>

Author: MichaelVerdon

packages/database/lib/modular/index.js

@@ -1,4 +1,7 @@
 import { getApp } from '@react-native-firebase/app';
+import DatabaseStatics from '../DatabaseStatics';
+
+const { ServerValue } = DatabaseStatics;
 
 /**
  * @typedef {import("..").FirebaseApp} FirebaseApp
@@ -109,15 +112,15 @@ export function getServerTime(db) {
  * @returns {object}
  */
 export function serverTimestamp() {
-  return firebase.database.ServerValue.TIMESTAMP;
+  return ServerValue.TIMESTAMP;
 }
 
 /**
  * @param {number} delta
  * @returns {object}
  */
 export function increment(delta) {
-  return firebase.database.ServerValue.increment(delta);
+  return ServerValue.increment(delta);
 }
 
 export * from './query';