ci: build stage4 and run behavior tests with it on x86_64-linux-debug(-llvm)
This was removed in 125a9aa82b55f8d1e2b6d08d61e697e6dfacbba6. But now that our
x86_64-linux machines have had their resources properly allocated, resulting in
runs taking 1-3 hours rather than 4-8, we can add this back.
faa485e630Alex Rønne Petersen committed on 1/5/2026, 2:41:16 PMparent962903e