Fix PR review issues: head.html test content, misleading test name, and missing try/finally

[Copilot]

Three issues flagged in code review on the brand-aware templates PR.

Changes

• lib/templates/email/head.html – Replaced committed test fixture string (<div>Test Head Template</div>) with a backward-compatibility comment; brand-specific templates under ionos/ are the intended path.

• tests/unit/BrandResolverTest.php – Renamed testGetBrandReturnsDefaultWhenNotConfigured → testGetBrandReturnsDefaultBrand (the test explicitly passes 'ionos', so it validates the default brand value, not an unconfigured state); assertion updated to use BrandResolver::DEFAULT_BRAND instead of the hardcoded string.

• tests/lib/EMailTemplateTest.php – Wrapped the file_put_contents write and all assertions in testIncludeTemplateFileIsCovered with try/finally to guarantee file restoration on assertion failure or exception:

file_put_contents($templateFile, $expectedContent);
try {
    // ... reset property, invoke method, assert ...
} finally {
    if ($originalContent !== null) {
        file_put_contents($templateFile, $originalContent);
    } else {
        unlink($templateFile);
    }
}

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