[4.0] Fix filtering banners by keywords

[SharkyKZ]

Summary of Changes

Fixes filtering banners by keywords. Similar to #29466.

Testing Instructions

Create a banner client.
Create a banner. Assign to a client. Add a keyword, e.g. Joomla.
Set some keywords for the document. Make sure the last keyword is not the same as the one set in the banner. E.g. add this to templates/cassiopeia/index.php:

$this->setMetadata('keywords', 'Joomla, CMS');

Publish a banner module. Enable Select by Keyword option.
View the module in frontend.

Expected result

Banner shown.

Actual result

Banner not shown.

Documentation Changes Required

[ChristineWk]

Was not sure where to add,
So, added above line (Instructions) templates/cassiopeia/index.php: to this place:
$app = Factory::getApplication();
$lang = $app->getLanguage();
$wa = $this->getWebAssetManager();
$this->setMetadata('keywords', 'Joomla, CMS');

[ChristineWk]

I have tested this item ✅ successfully on 1c6a570

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/29486.}

[wilsonge]

Thanks!