Bugfix/coep default header value

[GaProgMan]

Rationale for this PR

This PR fixes an issue where the default header for COEP (Cross-Origin-Embedder-Policy) was previously reported at same-require-corp but should have been require-corp.

PR Checklist

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Essential

These items are essential and must be completed for each commit. If they are not completed, the PR may not be accepted.

• [ ✅ ] I have added tests to the OwaspHeaders.Core.Tests project
• [ ✅ ] I have run the dotnet-format command and fixed any .editorconfig issues
• [ ✅ ] I have ensured that the code coverage has not dropped below 65%
• [ ✅ ] I have increased the version number in OwaspHeaders.Core.csproj (only relevant for code changes)

Optional

• [ ❎ ] I have documented the new feature in the docs directory
• [ ❎ ] I have provided a code sample, showing how someone could use the new code

Any Other Information

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[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
OwaspHeaders.Core	88%	74%	307	✔
OwaspHeaders.Core	88%	74%	307	✔
Summary	88% (1260 / 1440)	74% (298 / 400)	614	✔