Use DOTNET_ROLL_FORWARD: 'Major' for test-proxy

[danieljurek]

The macos-14 agent does not currently include .NET 6.x: https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md

.NET Core SDK: 7.0.102, 7.0.202, 7.0.306, 7.0.409, 8.0.101, 8.0.204, 8.0.300

Setting this variable ensures that test-proxy will run in environments which have later major versions of .NET Core.

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[weshaggard]

@scbedd are we not using the single exe version in our pipelines where this shouldn't be an issue?

[scbedd]

@scbedd are we not using the single exe version in our pipelines where this shouldn't be an issue?

Only java and cpp currently use the tool in pipeline, but it is used yes.

[weshaggard]

While I'm not opposed to this fix, I generally don't like force roll forward over majors. Could we also fix this issue by switching to the single exe for those not using it currently?

[danieljurek]

We could put this behind a parameter that defaults to false

[weshaggard]

We could put this behind a parameter that defaults to false

I don't think that is necessary but do you know why we cannot use the single exe for cpp?

[danieljurek]

Chatted w/ @weshaggard -- This can merge today. Wes' concerns include the fact that over time major version changes in frameworks can lead to breaks.

I opened #8387 to track having an eng/common YAML which installs the standalone exe.