Fatal error when using GLA 2.4.7 and flexible-shipping-ups plugin

[ianlin]

Describe the bug:

Reported in p1686202399910239-slack-C7U3Y3VMY and originally from the support forum.

GLA 2.4.7 uses psr/http-message 2.0 while the flexible-shipping-ups plugin uses 1.1. In 2.0 it adds function return types in the class interface and in GLA we didn't add prefix to psr/http-message library so the fatal error happened.

Here's the error:

2023-06-07T11:48:32+00:00 CRITICAL Declaration of UpsFreeVendor\GuzzleHttp\Psr7\Uri::getScheme() must be compatible with Psr\Http\Message\UriInterface::getScheme(): string in /home/795922.cloudwaysapps.com/axqxgxgnqn/public_html/wp-content/plugins/flexible-shipping-ups/vendor_prefixed/guzzlehttp/psr7/src/Uri.php on line 346

Steps to reproduce:

Note that I personally couldn't reproduce the error as I did not set up the UPS plugin properly. But from the log the root cause is obvious so we should add the prefix to psr/http-message library.

1. Install GLA 2.4.7 and flexible-shipping-ups plugin.
2. Go to wp-admin/admin.php?page=wc-settings&tab=shipping, add UPS Live Rates shipping method to the shipping zone you're testing.
3. Go to cart and checkout page, notice the fatal error.

Expected behavior:

There shouldn't be fatal error.

Actual behavior:

The fatal error appears and the site crashes.