missing $ for string interpolation

[tebeco]

Describe your changes

Error in CI/CD shows:

  AzureKeyVaultEmulator.TestContainers.Exceptions.KeyVaultEmulatorException : CRT is required for a Linux host machine but was missing at path: {pfxPath}.

Issue ticket number and link

No ticket was opened for this one

- throw new KeyVaultEmulatorException( "CRT .......... {pfxPath}.");
+ throw new KeyVaultEmulatorException($"CRT .......... {pfxPath}.");

Checklist before requesting a review

• I have performed a self-review of my code.
• I have ran the test suite locally to ensure no breaking changes have been added.
• I have not removed or changed Azure Key Vault endpoints which break SDK functionality.
• NOT APPLICABLE: I have added new tests, if applicable.

[Copilot]

Pull request overview

This PR fixes a string interpolation bug in an error message where the missing $ prefix caused the literal text {pfxPath} to be displayed instead of the actual path value.

Changes:

• Added the missing $ character for string interpolation in a KeyVaultEmulatorException error message