docs: Fix typos in libraries/caching.rst

[obozdag]

Description
Fix typos in libraries/caching.rst

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Why do you remove this?

[obozdag]

@kenjis Because in the code backupHandler is 'dummy'.

[kenjis]

Revert this change or update the description.

It is just the default value is dummy.
It explains file is often used for backup.

[kenjis]

Why do we need to add this?
Dummy is not a real cache handler. It does not cache anything.

[obozdag]

@kenjis $backupHandler is different in User guide and App/Config/Cache.php file. I tried to make them the same. Guide says $backupHandler is File but code has $backupHandler = 'dummy'. How should we match them? $handler = 'file', $backupHandler = 'dummy' in the code. Making two of them 'file' is a bit meaningless.

[kenjis]

The user guide does not say about the default backup handler.

The default $backupHandler should be dummy. Because it never fails to initialize.
And it does not cache anything, so it is the same as not using cache.

In real apps, it is often file and the primary cache is memcached or redis.
Because file can be used in most environments.

[obozdag]

@kenjis "The user guide does not say about the default backup handler."
Then I misunderstood this part "This is commonly the File handler". So, it means that we cannot match the user guide to code.

[kenjis]

Yes. If it is a bit difficult to understand,

1. show that the default handler is dummy
2. explain that file handler is often used