Update test suites

[glaxxie]

Simplify test files for:

• Armstrong Numbers
• Isbn Verifier -Isogram
• Matching Brackets
• Pangram

Simplify boolean test to be more in line with Pester's style.
Main purpose is to test the improved work flow change.

[no important files changed]

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!

[ErikSchierboom]

@glaxxie I merged this myself to make sure that the [no important files changed] was added (it has, in the past, occasionally been forgotten). Thanks for this!