Update Ubuntu 25.10 to 26.04 (#121730)

- Ubuntu 25.10 was added while it was in preview, in preparation for
26.04.
- 25.10 is now GA and 26.04 is in preview (been so for a while but the
official container release is new-ish and we are dependent on that)
- We'll validate CI relability in `main` and then move to servicing when
we're comfortable.

Author: richlander

eng/pipelines/helix-platforms.yml

@@ -121,9 +121,9 @@ variables:
     value: Ubuntu.2204.Amd64
 
   # Ubuntu x64
-  # Latest: 25.10
+  # Latest: 26.04
   - name: helix_linux_x64_ubuntu_latest
-    value: (Ubuntu.2510.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-25.10-helix-amd64
+    value: (Ubuntu.2604.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-amd64
 
   # Oldest: 22.04
   - name: helix_linux_x64_ubuntu_oldest
@@ -181,9 +181,9 @@ variables:
     value: (Debian.12.Arm32)Ubuntu.2204.ArmArch@mcr.microsoft.com/dotnet-buildtools/prereqs:debian-12-helix-arm32v7
 
   # Linux ARM64
-  # Latest: Ubuntu 25.10
+  # Latest: Ubuntu 26.04
   - name: helix_linux_arm64_latest
-    value: (Ubuntu.2510.ArmArch.Open)Ubuntu.2204.ArmArch.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-25.10-helix-arm64v8
+    value: (Ubuntu.2604.ArmArch.Open)Ubuntu.2204.ArmArch.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-arm64v8
 
   # Oldest: Ubuntu 22.04
   - name: helix_linux_arm64_oldest

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

@@ -29,7 +29,7 @@ jobs:
 
     # Linux arm64
     - ${{ if eq(parameters.platform, 'linux_arm64') }}:
-      - (Ubuntu.2510.Arm64.Open)AzureLinux.3.Arm64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-25.10-helix-arm64v8
+      - (Ubuntu.2604.Arm64.Open)AzureLinux.3.Arm64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-arm64v8
 
     # Linux musl x64
     - ${{ if eq(parameters.platform, 'linux_musl_x64') }}:

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

@@ -31,7 +31,7 @@ jobs:
     # Linux arm64
     - ${{ if eq(parameters.platform, 'linux_arm64') }}:
       - ${{ if or(eq(parameters.jobParameters.isExtraPlatformsBuild, true), eq(parameters.jobParameters.includeAllPlatforms, true)) }}:
-        - (Ubuntu.2510.ArmArch.Open)AzureLinux.3.Arm64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-25.10-helix-arm64v8
+        - (Ubuntu.2604.ArmArch.Open)AzureLinux.3.Arm64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-arm64v8
       - ${{ if or(ne(parameters.jobParameters.isExtraPlatformsBuild, true), eq(parameters.jobParameters.includeAllPlatforms, true)) }}:
         - (AzureLinux.3.0.ArmArch.Open)AzureLinux.3.Arm64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-helix-arm64v8
 
@@ -64,7 +64,7 @@ jobs:
             - (Debian.13.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:debian-13-helix-amd64
             - (Fedora.42.Amd64.Open)AzureLinux.3.Amd64.open@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-42-helix-amd64
             - (openSUSE.15.6.Amd64.Open)AzureLinux.3.Amd64.open@mcr.microsoft.com/dotnet-buildtools/prereqs:opensuse-15.6-helix-amd64
-            - (Ubuntu.2510.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-25.10-helix-amd64
+            - (Ubuntu.2604.Amd64.Open)AzureLinux.3.Amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-26.04-helix-amd64
 
           - ${{ if eq(parameters.jobParameters.testScope, 'outerloop') }}:
               # outerloop only CoreCLR