When using Matomo/Piwik integration, only integer website IDs can be used.
If using the "Protect Track ID" Matomo plugin (https://plugins.matomo.org/ProtectTrackID), website IDs are strings which the "_piwik.html.haml" layout file does not supports because it assumes "extra_config.piwik_site_id" variable contains an integer and prints it to JavaScript code without quotes.

This commits surrounds "extra_config.piwik_site_id" variable with double quotes (") so that it works with both integers and strings.

Issue: #61606