Update functional tests to use the PSR NullLogger

This avoids using the deprecated NullLogger in tests.
minor #13159 Update functional tests to use the PSR NullLogger (stof)

This PR was merged into the 2.3 branch.

Discussion
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Update functional tests to use the PSR NullLogger

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This avoids using the deprecated NullLogger in tests.

I'm applying this in 2.3 to make merging branches easier. This is especially needed for 2.7 because of deprecation warnings added in #13060 (tests are failing in this PR currently because of that)

Commits
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30cff26 Update functional tests to use the PSR NullLogger