Do not print summary repeatedly for each logger

[MatejKafka]

PR Summary

Updates the foreach loop where diagnostics are written to only write the summary once instead of once per logger. Given that the summary is always printed to the host (and not to the logger), it does not make sense to print it multiple times. Since there's only a single logger shipped with PSScriptAnalyzer, this does manifest in practice, but it's relevant for my follow-up PRs. :)

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.

[bergmeister]

Thanks, ran CI, looks good. Thoughts @andyleejordan ?

[andyleejordan]

Looks good, thanks.