[release/9.0.1xx] Upgrade latest Alpine to 3.21 for VMR builds (#45416)

Author: github-actions[bot]

eng/pipelines/templates/variables/vmr-build.yml

@@ -15,9 +15,9 @@ variables:
 - name: almaLinuxContainer
   value: mcr.microsoft.com/dotnet-buildtools/prereqs:almalinux-8-source-build
 - name: alpineLatestContainer
-  value: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.20-withnode
+  value: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.21-amd64
 - name: alpinePreviousContainer
-  value: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.19-WithNode
+  value: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.20-withnode
 - name: centOSStreamContainer
   value: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream9
 - name: fedoraContainer
@@ -50,9 +50,9 @@ variables:
 - name: almaLinuxName
   value: AlmaLinux8
 - name: alpineLatestName
-  value: Alpine320
+  value: Alpine321
 - name: alpinePreviousName
-  value: Alpine319
+  value: Alpine320
 - name: centOSStreamName
   value: CentOSStream9
 - name: fedoraName
@@ -69,9 +69,9 @@ variables:
 - name: linuxMuslArm64Rid
   value: linux-musl-arm64
 - name: alpineLatestX64Rid
-  value: alpine.3.20-x64
+  value: alpine.3.21-x64
 - name: alpinePreviousX64Rid
-  value: alpine.3.19-x64
+  value: alpine.3.20-x64
 - name: centOSStreamX64Rid
   value: centos.9-x64
 - name: fedoraX64Rid