chore(deps): update registry.suse.com/bci/dotnet-sdk docker tag to v8.0.21 (#2559)

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

Author: renovate[bot]

ci/images/Dockerfile.dotnet8

@@ -1,5 +1,5 @@
 # Base-image
-FROM registry.suse.com/bci/dotnet-sdk:8.0.20@sha256:255e01937ff1b7626e75ec87cf17a60b8e86437fb123f66e2c2f9c672bcd9309 AS base
+FROM registry.suse.com/bci/dotnet-sdk:8.0.21@sha256:980f77d6eb57252d9d486651f22aa4674a476c5a3b2dfd35b8322fb4c008cda6 AS base
 
 ARG GITHUB_URL=https://github.com
 ARG NODEJS_DIST_URL