… an unsupported type (Deuchnord)

This PR was merged into the 4.3 branch.

Discussion
----------

[Cache] Log a more readable message when trying to cache an unsupported type

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #29710   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        |

Improved the warning risen when trying to save something that has a non-supported type in the Simple cache.

For instance, let's say the following code:
```php
class TestCommand extends Command
{
    private $cache;

    public function __construct(CacheInterface $cache)
    {
        parent::__construct();
        $this->cache = $cache;
    }

    // ...

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        $n = $this->cache->get('n', function () {
            return function () {
                return rand(0,10);
            };
        });

        dump($n());
    }
}
```

Running this code will give the following:
```
14:32:03 WARNING   [cache] Could not save key "n" in cache: the Closure type is not supported.
0
```

Commits
-------

21ba3c0 [Cache] Log a more readable error message when saving into cache fails

This PR was merged into the 4.3 branch.

Discussion
----------

[Cache] improve logged messages

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This was improved already in #31395, but the patch was incomplete.
This PR fixes this.

Commits
-------

257f3f1 [Cache] improve logged messages

This PR was squashed before being merged into the 4.3 branch (closes #31864).

Discussion
----------

[Cache] Fixed undefined variable in ArrayTrait

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

So once again (see #29591) my test suite managed to find an error in ArrayTrait in cache. This time it was this PR: #31395 later improved by #31590 that introduced `$id` to logging, which I guess should be `$key`? So this PR changes it to `$key`, ~but my tests **still fail** as there is no `$this->namespace` in `ArrayAdapter` (is this the only class that uses this ArrayTrait?). But I don't know what to do about it. Maybe @nicolas-grekas has some answers?~

Commits
-------

8568923 [Cache] Fixed undefined variable in ArrayTrait