Bump dotnet/sdk from 8.0 to 9.0 in the docker group

Bumps the docker group with 1 update: dotnet/sdk.


Updates `dotnet/sdk` from 8.0 to 9.0

---
updated-dependencies:
- dependency-name: dotnet/sdk
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: docker
...

Signed-off-by: dependabot[bot] <support@github.com>

sequester.Dockerfile

@@ -1,10 +1,10 @@
-FROM mcr.microsoft.com/dotnet/sdk:8.0 as build-env
+FROM mcr.microsoft.com/dotnet/sdk:9.0 as build-env
 # Copy everything and publish the release (publish implicitly restores and builds)
 WORKDIR /app
 COPY . ./
 RUN dotnet publish "actions/sequester/ImportIssues/ImportIssues.csproj" -c Release -o out --no-self-contained
 
 # Relayer the .NET SDK, anew with the build output
-FROM mcr.microsoft.com/dotnet/sdk:8.0
+FROM mcr.microsoft.com/dotnet/sdk:9.0
 COPY --from=build-env /app/out .
 ENTRYPOINT [ "dotnet", "/ImportIssues.dll" ]

whatsnew.Dockerfile

@@ -1,10 +1,10 @@
-FROM mcr.microsoft.com/dotnet/sdk:8.0 as build-env
+FROM mcr.microsoft.com/dotnet/sdk:9.0 as build-env
 # Copy everything and publish the release (publish implicitly restores and builds)
 WORKDIR /app
 COPY . ./
 RUN dotnet publish "WhatsNew.Cli/WhatsNew.Cli.csproj" -c Release -o out --no-self-contained
 
 # Relayer the .NET SDK, anew with the build output
-FROM mcr.microsoft.com/dotnet/sdk:8.0
+FROM mcr.microsoft.com/dotnet/sdk:9.0
 COPY --from=build-env /app/out .
 ENTRYPOINT [ "dotnet", "/WhatsNew.dll" ]