Tracking: Ubuntu 26.04 VM Plan

[richlander]

We currently have a policy of runing both Azure Linux and Ubuntu VMs. We use both VM types of bare VM testing. In the past, we've found subtle differences in that scenario. We also use the Azure Linux VMs as our container host.

This PR removes the Ubuntu VMs: dotnet/dotnet-buildtools-prereqs-docker#1606

This is a short term change to enable 26.04 testing in PR now. We'll switch back to VMs 26.04 VMs are ready (Mayish).

Azure VM Gallery: https://learn.microsoft.com/azure/virtual-machines/linux/endorsed-distros#platform-image-partners

@agocke

[dotnet-policy-service]

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[jkotas]

This change is "bad".

Why?

It was done for two reasons:

What are the two reasons? The list that follows has 5 bullet points...

[richlander]

It's not actually bad, hence the scare quotes.

We are losing Ubuntu VM testing until we get Ubuntu 26.04 VMs (ideally May). We are gaining 26.04 container coverage in trade w/no change to our cost envelope.

[richlander]

@hoyosjs