[StaticWebAssets] Add file to FileWrites even when the content is the same in OverrideHtmlAssetPlaceholders

[maraf]

Fixes bug with incremental clean.
We need to mark the file as "written to" even if we skipped the write because the content was the same.

[dotnet-policy-service]

Thanks for your PR, @@maraf.
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[Copilot]

Pull Request Overview

This PR ensures that files are marked as written in fileWrites even when their content hasn’t changed, fixing an incremental clean bug.

• Always calls PersistFileIfChanged and unconditionally adds outputPath to fileWrites
• Removes the conditional block around fileWrites.Add

Comments suppressed due to low confidence (1)

src/StaticWebAssetsSdk/Tasks/OverrideHtmlAssetPlaceholders.cs:97

• Add a unit test that covers the scenario where PersistFileIfChanged returns false (unchanged content) and verifies that fileWrites still contains outputPath to prevent future regressions.

fileWrites.Add(outputPath);