[ci] Upgrade docker env to bullseye. (#349)

Description
Upgrade docker env to bullseye.
Upgrade .NET to 7.0 to match bullseye.

azure-pipelines.yml

@@ -23,8 +23,8 @@ pool:
 
 resources:
   containers:
-  - container: sonic-slave-buster
-    image: sonicdev-microsoft.azurecr.io:443/sonic-slave-buster:latest
+  - container: sonic-slave-bullseye
+    image: sonicdev-microsoft.azurecr.io:443/sonic-slave-bullseye:latest
 
 parameters:
 - name: project_list
@@ -60,7 +60,7 @@ parameters:
 
 jobs:
   - job: build_test
-    container: sonic-slave-buster
+    container: sonic-slave-bullseye
     variables:
       sourceBranch: "$(Build.SourceBranch)"
     steps:
@@ -86,17 +86,16 @@ jobs:
 
     - script: |
         set -xe
-        sudo apt-get -y purge libhiredis-dev libnl-3-dev libnl-route-3-dev
+        sudo apt-get -y purge libhiredis-dev libnl-3-dev libnl-route-3-dev || true
         sudo dpkg -i libnl-3-200_*.deb
         sudo dpkg -i libnl-genl-3-200_*.deb
         sudo dpkg -i libnl-route-3-200_*.deb
         sudo dpkg -i libnl-nf-3-200_*.deb
         sudo dpkg -i libhiredis0.14_*.deb
         sudo dpkg -i libyang_1.0.73_amd64.deb
         sudo dpkg -i libswsscommon_1.0.0_amd64.deb
-        sudo dpkg -i python-swsscommon_1.0.0_amd64.deb
         sudo dpkg -i python3-swsscommon_1.0.0_amd64.deb
-      workingDirectory: $(Pipeline.Workspace)/target/debs/buster/
+      workingDirectory: $(Pipeline.Workspace)/target/debs/bullseye/
       displayName: 'Install Debian dependencies'
 
     - script: |
@@ -107,16 +106,16 @@ jobs:
         sudo pip3 install sonic_yang_models-1.0-py3-none-any.whl
         sudo pip3 install sonic_config_engine-1.0-py3-none-any.whl
         sudo pip3 install sonic_platform_common-1.0-py3-none-any.whl
-      workingDirectory: $(Pipeline.Workspace)/target/python-wheels/buster/
+      workingDirectory: $(Pipeline.Workspace)/target/python-wheels/bullseye/
       displayName: 'Install Python dependencies'
 
     - script: |
         set -ex
         # Install .NET CORE
         curl -sSL https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -
-        sudo apt-add-repository https://packages.microsoft.com/debian/10/prod
+        sudo apt-add-repository https://packages.microsoft.com/debian/11/prod
         sudo apt-get update
-        sudo apt-get install -y dotnet-sdk-5.0
+        sudo apt-get install -y dotnet-sdk-7.0
       displayName: "Install .NET CORE"
 
     - ${{ each project in parameters.project_list }}: