Fixed deprecated var interpolation style in Caching ContentHandler

[adriendupuis]

Question	Answer
JIRA issue	N/A
Type	bug
Target Ibexa version	v4.4.x
BC breaks	no

Changes suggested by https://www.php.net/manual/en/migration82.deprecated.php#migration82.deprecated.core.dollar-brace-interpolation

Avoid the following warnings when running on PHP 8.2:

• Deprecated: Using ${var} in strings is deprecated, use {$var} instead in /var/www/vendor/ibexa/core/src/lib/Persistence/Cache/ContentHandler.php on line 134
• Deprecated: Using ${var} in strings is deprecated, use {$var} instead in /var/www/vendor/ibexa/core/src/lib/Persistence/Cache/ContentHandler.php on line 241

Checklist:

• Provided PR description.
• Tested the solution manually.
• Provided automated test coverage.
• Checked that target branch is set correctly (main for features, the oldest supported for bugs).
• Ran PHP CS Fixer for new PHP code (use $ composer fix-cs).
• Asked for a review (ping @ibexa/engineering).

[alongosz]

Congrats on your first contribution to the Core @adriendupuis 🎉
The change is good as long as our Continuous Integration in the PR passes.
However there is a bit of standardization that applies to Product PRs, especially core

First of all, do you want to see this change in 4.3, 4.4, or the upcoming 4.5 (end of March)? This is important because we need to know when and to which branch to merge it.

Secondly, PR title should be formed in past simple, stating what has been changed, for instance:

Fixed deprecated var interpolation style in Caching ContentHandler

because once merged, that message describes history.

Side: Usually PR title should be prefixed with IBX JIRA issue number followed by colon, but for such small change in this case it's not necessary.

[mikadamczyk]

A commit message could be more descriptive

[adriendupuis]

Duplicate #205