CodeQL scanning fails due to autobuild not supporting go1.21

[ctlong]

Error log from GH action:

  2023/09/05 15:47:49 Autobuilder was built with go1.20.7, environment has go1.20.7
...
  2023/09/05 15:47:49 Error running go tooling: err: exit status 1: stderr: go: errors parsing go.mod:
  /home/runner/work/cf-smoke-tests/cf-smoke-tests/go.mod:5: unknown directive: toolchain
  
  2023/09/05 15:47:49 Extraction failed: exit status 1
  Error: We were unable to automatically build your code. Please replace the call to the autobuild action with your custom build steps. Encountered a fatal error while running "/opt/hostedtoolcache/CodeQL/2.14.3/x64/codeql/go/tools/autobuild.sh". Exit code was 1 and error was: 2023/09/05 15:47:49 Autobuilder was built with go1.20.7, environment has go1.20.7

We could replace autobuild with our own buildstep, or let it fail until CodeQL supports go1.21.