Fix: Not possible to create multiple Piwik tracker instances having different API urls

[lutdev]

Description

Fix for the issue https://github.com/matomo-org/matomo-php-tracker/issues/14

Checklist

• [✔/✖/NA] I have understood, reviewed, and tested all AI outputs before use
• [✔/✖/NA] All AI instructions respect security, IP, and privacy rules

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behaviour of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] New documentation added or existing documentation updated