Add support for Truffle dry run fork

Truffle has a dry run option on migration that forks the network to check the migration.

When deploying a contract with dry run skipped, and then attempting to do an upgrade with dry run, the upgrade fails with:

Error: Proxy admin is not the one registered in the network manifest
    at upgradeProxy

Using Box.sol and BoxV2.sol from https://forum.openzeppelin.com/t/openzeppelin-upgrades-step-by-step-tutorial-for-truffle/3579 and the deploy and upgrade migrations below:

2_deploy_box.js

// migrations/2_deploy_box.js
const Box = artifacts.require('Box');
 
const { deployProxy } = require('@openzeppelin/truffle-upgrades');
 
module.exports = async function (deployer) {
  await deployProxy(Box, [42], { deployer, initializer: 'store' });
};

3_upgrade_box.js

// migrations/3_upgrade_box.js
const Box = artifacts.require('Box');
const BoxV2 = artifacts.require('BoxV2');

const { upgradeProxy } = require('@openzeppelin/truffle-upgrades');
 
module.exports = async function (deployer) {
  const box = await Box.deployed();
  await upgradeProxy(box.address, BoxV2, { deployer });
};

$ npx truffle migrate --network rinkeby --to 2 --skip-dry-run
...
Starting migrations...
======================
> Network name:    'rinkeby'
> Network id:      4
> Block gas limit: 10000000 (0x989680)


1_initial_migration.js
...
2_deploy_box.js
===============

   Deploying 'Box'
   ---------------
   > transaction hash:    0x55fe331e1997c5ee4233fb9db21eb63bb12c0d9aac02ba21750cca487364e903
   > Blocks: 2            Seconds: 21
   > contract address:    0xE1a1b97E43362F8FE6F08Bc3A6EC250C35146E0F
...
   Deploying 'ProxyAdmin'
   ----------------------
   > transaction hash:    0x725e4486c35d4b6c812513a5705e9c04ea3b0ed19ebb6cedd443dc5c371709c6
   > Blocks: 1            Seconds: 17
   > contract address:    0xe34E320E784D56728aC0247005De168bdDA17beE
...
   Deploying 'AdminUpgradeabilityProxy'
   ------------------------------------
   > transaction hash:    0xc1210bfcb6381dd24ac590b3e93820ba49700207affcb6cea0550eb94318698a
   > Blocks: 1            Seconds: 17
   > contract address:    0xe2e88690f2F3CAC2534412AaA5C93e8b6368Ad98
...

$ npx truffle migrate --network rinkeby

Compiling your contracts...
===========================
...

Migrations dry-run (simulation)
===============================
> Network name:    'rinkeby-fork'
> Network id:      4
> Block gas limit: 10000000 (0x989680)


3_upgrade_box.js
================

Error: Proxy admin is not the one registered in the network manifest
    at upgradeProxy (/home/abcoathup/projects/forum/truffledryrun/node_modules/@openzeppelin/truffle-upgrades/src/upgrade-proxy.ts:76:11)
Truffle v5.1.54 (core: 5.1.54)
Node v10.22.1

Reproduce the failure with the two Truffle migration commands and the Box/BoxV2 example. Start at src/upgrade-proxy.ts:76, where the manifest proxy-admin check fails during the dry-run fork. Done means the upgrade migration succeeds after the initial deployment was run with --skip-dry-run, while preserving the existing network-manifest validation.