Upgrade to .NET 9

[BNAndras]

See exercism/vbnet-test-runner#49 and https://forum.exercism.org/t/upgrade-to-net-9/15843/2. This should be merged in tandem with the test runner PR.

The first commit standardizes vbprojs and bumps the package versions to match what the test runner will use.

The second commit resolves an XUnit bug where arrays can't be directly compared with Assert.Equal for VB.

The third commit flips the expected and actual argument order for Bob.

The fourth commit resolves an ambiguous match exception for comparing two strings. That only affects Bob and Two-Fer for some reason, but I needed to chose a more specific overload. I chose the one that takes a Boolean to set whether case should be ignored.

[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]

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[BNAndras]

@ErikSchierboom, no rush but as the .NET expert around here, do the second and fourth commits make sense to you? Or should I try something else to resolve the issues?

[ErikSchierboom]

For the first one, I'm not sure I like that approach as it is unclear to me what's happening. Maybe either extract the expected value to a variable or cast it to a string?

For the second one I'd probably have gone the route of specifying the type for the expected variable, but it's fine.

[ErikSchierboom]

I've left some comments on the test runner PR.