GPU Workflow: Avoid duplicated variable

[davidrohr]

@shahor02 : Some simplification of the dump

[github-actions]

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[alibuild]

Error while checking build/O2/fullCI_slc9 for 1152104 at 2026-03-11 11:03:

## sw/BUILD/O2-latest/log
/sw/SOURCES/O2/15144-slc9_x86-64/0/GPU/Workflow/src/GPUWorkflowSpec.cxx:815:18: error: no match for 'operator&&' (operand types are 'bool' and 'o2::framework::ProcessingContext')
/sw/SOURCES/O2/15144-slc9_x86-64/0/GPU/Workflow/src/GPUWorkflowSpec.cxx:815:29: error: base operand of '->' has non-pointer type 'o2::framework::ProcessingContext'
/sw/SOURCES/O2/15144-slc9_x86-64/0/GPU/Workflow/src/GPUWorkflowSpec.cxx:815:46: error: expected primary-expression before 'const'
/sw/SOURCES/O2/15144-slc9_x86-64/0/GPU/Workflow/src/GPUWorkflowSpec.cxx:815:46: error: expected ')' before 'const'
/sw/SOURCES/O2/15144-slc9_x86-64/0/GPU/Workflow/src/GPUWorkflowSpec.cxx:816:86: error: base operand of '->' has non-pointer type 'o2::framework::ProcessingContext'
/sw/SOURCES/O2/15144-slc9_x86-64/0/GPU/Workflow/src/GPUWorkflowSpec.cxx:816:103: error: expected primary-expression before 'const'
ninja: build stopped: subcommand failed.

Full log here.