Show all dependent modules on module confirm form for each chosen module

Thanks for the patch, the underlying fix looks correct to me. A few small
things before this is RTBC:

1. $checked = array_keys($modules['install']); followed by
in_array($dependency, $checked) does an O(n) scan for every dependency checked. Since $modules['install'] is already keyed by module name, it would be cheaper - and more consistent with the isset() checks used elsewhere in this method - to just copy the array and look up the key directly, e.g.:

  $original_install = $modules['install'];
     ...
     if (!isset($original_install[$dependency]) && ...)

2. It would help to add a short comment explaining why the snapshot needs to be taken before the loop starts. It's not obvious from the code alone, and without an explanation a future refactor could simplify this back to checking $modules['install'] directly and reintroduce the bug this patch is fixing.

3. There's a stray blank line before the closing brace of testModuleDependencyMessages() in DependencyTest.php, phpcs will likely flag it.

I have a minor comment on grammar, but I'm confused by this, I just compared this branch and main.

I ran drush si then tried installing search node and Json response validator:
Main:

    You must install the following modules to install JSON:API Response Validator:
        JSON:API
        Serialization
    You must install the following module to install Search node:
        Search

Would you like to continue with the above? 

This branch:

    You must install the following modules to install JSON:API Response Validator:
        JSON:API
        Serialization
    You must install the following module to install Search node:
        Search

Would you like to continue with the above? 

What case is this not showing the right list?

Is it about showing dependencies in more than one list? I uninstalled many modules so I could install block content and navigation which both depend on block.
Main:

    You must install the following modules to install Block Content:
        Block
        Text
    You must install the following modules to install Navigation:
        Layout Builder
        Layout Discovery

Would you like to continue with the above? 

This branch:

    You must install the following modules to install Block Content:
        Block
        Text
    You must install the following modules to install Navigation:
        Block
        Layout Builder
        Layout Discovery

Would you like to continue with the above? 

That seems to be the case so I updated the title.

The before and after in the IS don't load, but I have the before and after text here so I think that's ok.

I also can't run the test only, but the test does look good, @quietone, if you could runt the test only that would be great.