dpl-workflow.sh: using MI100 serialization workaround by default again, with option to disable it with env var

[ehellbar]

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[github-actions]

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[alibuild]

Error while checking build/O2/fullCI_slc9 for d4814fb at 2025-05-21 07:11:

## sw/BUILD/O2-full-system-test-latest/log
command /sw/slc9_x86-64/O2/14302-slc9_x86-64-local1/prodtests/full-system-test/dpl-workflow.sh had nonzero exit code 2

Full log here.