Add Attestations to build and release workflow

[GaProgMan]

Rationale for this PR

This PR adds the required steps to the default build script which will attempt to add attestations to the built nuget package.

Note

This is (currently) only running in the dotnet.yml file (aka: "Build Repo"). Once confirmed as working, the changes will be ported to the release.yml file (aka "Release").

PR Checklist

Feel free to either check the following items (by place an x inside of the square brackets) or by replacing the square brackets with a relevant emoji from the following list:

• ✅ to indicate that you have checked something off
• ❎ to indicate that you haven't checked something off
• ❓ to indicate that something might not be relevant (writing tests for documentation changes, for instance)

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

This section is optional, but it might be useful to list any other information you think is relevant.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
OwaspHeaders.Core	87%	73%	276	✔
OwaspHeaders.Core	87%	73%	276	✔
Summary	87% (1106 / 1276)	73% (264 / 360)	552	✔