Pin mcr.microsoft.com/dotnet/sdk Docker tag to c7445f1

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.devcontainer/Dockerfile

@@ -1,5 +1,5 @@
 # Refer to https://hub.docker.com/_/microsoft-dotnet-sdk for available versions
-FROM mcr.microsoft.com/dotnet/sdk:10.0.100
+FROM mcr.microsoft.com/dotnet/sdk:10.0.100@sha256:c7445f141c04f1a6b454181bd098dcfa606c61ba0bd213d0a702489e5bd4cd71
 
 # Installing mono makes `dotnet test` work without errors even for net472.
 # But installing it takes a long time, so it's excluded by default.