Fix a PIX pass's attempt to set the validator version

[jeffnn]

This pass was attempting to compare different things. The return values of GetDxilVersion are not shader models, but... dxil version. Since the code is trying to upgrade the validator version, I changed this to GetValidatorVersion, to pair with SetValidatorVersion.
The previous code was breaking the nvidia driver on workgraphs.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[bob80905]

Though I also don't understand the reasoning, the code and tests look correct. Although I would personally put a blurb on top of each test specifying why each test exists. (Like for example, in validatorNoDowngrade, "This test tests that a shader with dxil validator version of 1.8 does not downgrade to 1.4" and for validatorUpgrade "This test tests that a shader with dxil validator version of 1.3 gets upgraded to 1.4 after the annotate with virtual regs pass.")

[jeffnn]

Though I also don't understand the reasoning, the code and tests look correct. Although I would personally put a blurb on top of each test specifying why each test exists. (Like for example, in validatorNoDowngrade, "This test tests that a shader with dxil validator version of 1.8 does not downgrade to 1.4" and for validatorUpgrade "This test tests that a shader with dxil validator version of 1.3 gets upgraded to 1.4 after the annotate with virtual regs pass.")

Good idea. Your comment suggestions used, almost verbatim

[tex3d]

The change looks fine, though I still don't know why the validator version was upgraded in the first place.