[mlir][GPU] Fix double spaces in tests after ODS printer fix. NFC. (#185325)
Follow-up to #184253. The ODS attr/type printer fix removed the leading
space from generated print() methods. Update tests that checked for the
old double-space output of GPU ops using GPU_DimensionAttr and
GPU_MmaElementwiseOpAttr.
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>