GH-34661: [CI][C#] Update Ubuntu C# jobs to use image with .NET 7.0 (#…

…34662)

### Rationale for this change
Nightly nuget jobs is failing since we updated our release verification to use .NET 7.0

### What changes are included in this PR?

Update docker image used to use .NET 7.0

### Are these changes tested?

Will trigger jobs via archery

### Are there any user-facing changes?

No
* Closes: #34661

Authored-by: Raúl Cumplido <raulcumplido@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

.env

@@ -56,7 +56,7 @@ UBUNTU=20.04
 CLANG_TOOLS=14
 CUDA=11.0.3
 DASK=latest
-DOTNET=6.0
+DOTNET=7.0
 GCC_VERSION=""
 GO=1.17
 STATICCHECK=v0.2.2

ci/docker/ubuntu-20.04-csharp.dockerfile → ci/docker/ubuntu-22.04-csharp.dockerfile

@@ -17,7 +17,7 @@
 
 ARG arch=amd64
 ARG dotnet=7.0
-ARG platform=focal
+ARG platform=jammy
 FROM mcr.microsoft.com/dotnet/sdk:${dotnet}-${platform}-${arch}
 
 RUN dotnet tool install --tool-path /usr/local/bin sourcelink

docker-compose.yml

@@ -1538,16 +1538,16 @@ services:
     # Usage:
     #   docker-compose build ubuntu-csharp
     #   docker-compose run ubuntu-csharp
-    image: ${REPO}:${ARCH}-ubuntu-20.04-csharp-${DOTNET}
+    image: ${REPO}:${ARCH}-ubuntu-22.04-csharp-${DOTNET}
     build:
       context: .
-      dockerfile: ci/docker/ubuntu-20.04-csharp.dockerfile
+      dockerfile: ci/docker/ubuntu-22.04-csharp.dockerfile
       cache_from:
-        - ${REPO}:${ARCH}-ubuntu-20.04-csharp-${DOTNET}
+        - ${REPO}:${ARCH}-ubuntu-22.04-csharp-${DOTNET}
       args:
         arch: ${ARCH}
         dotnet: ${DOTNET}
-        platform: focal
+        platform: jammy
     shm_size: *shm-size
     volumes: *ubuntu-volumes
     command: &csharp-command >