[release/10.0] Upgrade Ubuntu 22.04 Helix queues to 26.04 containers (#125997)

> [!NOTE]
> This PR was AI/Copilot-generated.

Replace bare Ubuntu 22.04 VM Helix queue references with Ubuntu 26.04
container equivalents hosted on AzureLinux 3.

- Mono path: `Ubuntu.2204.Amd64.Open` VM → `ubuntu-26.04-helix-amd64`
container
- CoreCLR general set: `Ubuntu.2204.Amd64.Open` VM →
`ubuntu-26.04-helix-amd64` container (promoted from extra-platforms)
- Remove redundant 26.04 entry from extra-platforms
- Fix `AzureLinux.3.Amd64.open` → `AzureLinux.3.Amd64.Open` casing on
Fedora, openSUSE, and AzureLinux host VM names

Not changed (intentionally):
- Android queues (`Ubuntu.2204.Amd64.Android.*`)
- WASM/WASI container references
- ARM container host VMs

Backport of #125535.

Ref #125748, #125690

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: richlander

eng/pipelines/libraries/helix-queues-setup.yml

@@ -56,24 +56,23 @@ jobs:
       - ${{ else }}:
         - ${{ if eq(parameters.jobParameters.runtimeFlavor, 'mono') }}:
           # Mono path - test minimal scenario
-          - Ubuntu.2204.Amd64.Open
+          - (Ubuntu.2604.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-amd64
         - ${{ else }}:
         # CoreCLR path
           - ${{ if and(eq(parameters.jobParameters.isExtraPlatformsBuild, true), ne(parameters.jobParameters.testScope, 'outerloop'))}}:
             # extra-platforms CoreCLR (inner loop only)
             - (Debian.13.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:debian-13-helix-amd64
-            - (Fedora.43.Amd64.Open)AzureLinux.3.Amd64.open@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-43-helix-amd64
-            - (openSUSE.16.0.Amd64.Open)AzureLinux.3.Amd64.open@mcr.microsoft.com/dotnet-buildtools/prereqs:opensuse-16.0-helix-amd64
-            - (Ubuntu.2604.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-amd64
+            - (Fedora.43.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-43-helix-amd64
+            - (openSUSE.16.0.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:opensuse-16.0-helix-amd64
 
           - ${{ if eq(parameters.jobParameters.testScope, 'outerloop') }}:
               # outerloop only CoreCLR
               - AzureLinux.3.Amd64.Open
 
           - ${{ if or(ne(parameters.jobParameters.isExtraPlatformsBuild, true), eq(parameters.jobParameters.includeAllPlatforms, true))}}:
               # inner and outer loop CoreCLR (general set)
-              - Ubuntu.2204.Amd64.Open
-              - (AzureLinux.3.0.Amd64.Open)AzureLinux.3.Amd64.open@mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-helix-amd64
+              - (Ubuntu.2604.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-amd64
+              - (AzureLinux.3.0.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-helix-amd64
               - (Centos.10.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream-10-helix-amd64
 
     # OSX arm64