fixing build

.circleci/config.yml

@@ -21,7 +21,7 @@ jobs:
     # from build_android_and_ios. However, setting up the Linux build is so much faster than the Mac host that
     # it's better to let this one run independently so we can get quick CI feedback for any basic problems.
     docker:
-      - image: mcr.microsoft.com/dotnet/sdk:7.0-focal
+      - image: mcr.microsoft.com/dotnet/sdk:7.0
     environment:
       ASPNETCORE_SUPPRESSSTATUSMESSAGES: "true" # suppresses annoying debug output from embedded HTTP servers in tests
       TEST_HARNESS_PARAMS: -junit /tmp/circle-reports/contract-tests-junit.xml