trusted signing: add filter to sign files with .cip extension

[Jaxelr]

Description

This PR expands the Az.TrustedSigning module to also support Signing .cip files along with .bin files for signing ci policies.

cc: @janielMartell

Mandatory Checklist

• Please choose the target release of Azure PowerShell. (⚠️Target release is a different concept from API readiness. Please click below links for details.)

  • General release
  • Public preview
  • Private preview
  • Engineering build
  • No need for a release

• Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD update ChangeLog.md file(s) appropriately
  • Update src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md.
    • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

[azure-client-tools-bot-prd]

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[Copilot]

Pull Request Overview

This PR adds support for signing .cip files alongside .bin files in the Az.TrustedSigning module.

• Added a null-environment check with an exception in CodeSigningServiceClient.
• Extended InvokeCIPolicySigning.ValidateFileType to recognize .cip files and updated messaging.
• Updated ChangeLog.md to document .cip extension support.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/TrustedSigning/TrustedSigning/Models/CodeSigningServiceClient.cs	Throw ArgumentException when context.Environment is null
src/TrustedSigning/TrustedSigning/Commands/InvokeCIPolicySigning.cs	Accept .cip extension in ValidateFileType and adjust warning text
src/TrustedSigning/TrustedSigning/ChangeLog.md	Added entry for .cip support in upcoming release

Comments suppressed due to low confidence (2)

src/TrustedSigning/TrustedSigning/Commands/InvokeCIPolicySigning.cs:145

• There should be automated tests covering .cip extension handling in ValidateFileType to ensure new behavior is verified.

            string fileExtension = System.IO.Path.GetExtension(fullInPath);

src/TrustedSigning/TrustedSigning/Commands/InvokeCIPolicySigning.cs:147

• [nitpick] The indentation for the second OR condition is inconsistent. Align it under the first string.Equals for better readability.

                     string.Equals(fileExtension, ".cip", StringComparison.OrdinalIgnoreCase))

[YanaXu]

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