dsl: Dimension off by one mistake

[JDBetteridge]

As reported by Dylan Stark, an off-by-one in ConditionalDimension._arg_defaults breaks decoupler time_M reduction.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.18%. Comparing base (8c448dc) to head (dab7d2a).
⚠️ Report is 2 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (8c448dc) and HEAD (dab7d2a). Click for more details.

HEAD has 12 uploads less than BASE

Flag	BASE (8c448dc)	HEAD (dab7d2a)
	18	9
pytest-gpu-gcc-	6	4
pytest-gpu-icx-	3	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2881       +/-   ##
===========================================
- Coverage   83.44%   52.18%   -31.26%     
===========================================
  Files         248      242        -6     
  Lines       51311    50751      -560     
  Branches     4428     4402       -26     
===========================================
- Hits        42817    26485    -16332     
- Misses       7738    23317    +15579     
- Partials      756      949      +193     

Flag	Coverage Δ
pytest-gpu-aomp-amdgpuX	68.81% <100.00%> (ø)
pytest-gpu-gcc-	43.46% <0.00%> (-34.58%)	⬇️
pytest-gpu-icx-	43.31% <0.00%> (-34.34%)	⬇️
pytest-gpu-nvc-nvidiaX	69.33% <100.00%> (+0.01%)	⬆️

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[EdCaunt]

Seems reasonable once green

[JDBetteridge]

Adding the invalid label as the initial bug report may have been incorrect

[mloubout]

Fixed in #2883