C#: Update rules_dotnet to 0.21.5.

Author: michaelnebel

MODULE.bazel

@@ -26,7 +26,7 @@ bazel_dep(name = "nlohmann_json", version = "3.11.3", repo_name = "json")
 bazel_dep(name = "fmt", version = "10.0.0")
 bazel_dep(name = "rules_kotlin", version = "2.1.3-codeql.1")
 bazel_dep(name = "gazelle", version = "0.40.0")
-bazel_dep(name = "rules_dotnet", version = "0.19.2-codeql.1")
+bazel_dep(name = "rules_dotnet", version = "0.21.5")
 bazel_dep(name = "googletest", version = "1.14.0.bcr.1")
 bazel_dep(name = "rules_rust", version = "0.66.0")
 bazel_dep(name = "zstd", version = "1.5.5.bcr.1")
@@ -172,7 +172,7 @@ http_archive(
 )
 
 dotnet = use_extension("@rules_dotnet//dotnet:extensions.bzl", "dotnet")
-dotnet.toolchain(dotnet_version = "9.0.300")
+dotnet.toolchain(dotnet_version = "10.0.100")
 use_repo(dotnet, "dotnet_toolchains")
 
 register_toolchains("@dotnet_toolchains//:all")