Fix Code Coverage Tests

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

Our code coverage CI build was failing due to an introduced reliance on DebugSaveXX working correctly in all build environments.

Since we no longer run the coverage tests against PRs directly it's best just to remove the condition.

[Copilot]

Pull Request Overview

This PR fixes failing code coverage tests by removing a conditional block that bypassed image saving when running under code coverage.

• Removed early return conditions checking TestEnvironment.RunsWithCodeCoverage in DebugSave and DebugSaveMultiFrame methods.
• Updated using statement syntax to the newer declaration style for improved consistency.

Comments suppressed due to low confidence (2)

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs:292

• Confirm that the new using declaration syntax is supported in your project's targeted C# version and applied consistently across the codebase.

using Image<TPixel> debugImage = GetDebugOutputImageMultiFrame<TPixel>(...

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs:300

• Ensure that the updated using declaration style is consistently used for resource management throughout the repository to avoid style discrepancies.

using Image<TPixel> referenceImage = GetReferenceOutputImageMultiFrame<TPixel>(...