Bump dotnet/sdk

Bumps the dotnet-images group with 1 update in the /docker/migrate directory: dotnet/sdk.


Updates `dotnet/sdk` from 9.0.313 to 9.0.315

---
updated-dependencies:
- dependency-name: dotnet/sdk
  dependency-version: 9.0.314
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dotnet-images
...

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

Author: dependabot[bot]

docker/migrate/Dockerfile

@@ -1,7 +1,7 @@
 # Migration Job Dockerfile
 # Cloud Run Job でマイグレーションを実行するためのイメージ
 
-FROM mcr.microsoft.com/dotnet/sdk:9.0.313 AS build
+FROM mcr.microsoft.com/dotnet/sdk:9.0.315 AS build
 WORKDIR /src
 
 # プロジェクトファイルをコピーして依存関係を復元