fix(test): Run is an index, not a label

tools/schemacode/src/bidsschematools/tests/data/expected_bids_validator_xs_write.log

@@ -1,7 +1,7 @@
 
 SUMMARY:
 0 out of 1 files were successfully validated, using the following regular expressions:
-	- `.*?/sub-(?P<subject>[0-9a-zA-Z+]+)/(|ses-(?P<session>[0-9a-zA-Z+]+)/)anat/sub-(?P=subject)(|_ses-(?P=session))(|_acq-(?P<acquisition>[0-9a-zA-Z+]+))(|_ce-(?P<ceagent>[0-9a-zA-Z+]+))(|_rec-(?P<reconstruction>[0-9a-zA-Z+]+))(|_run-(?P<run>[0-9a-zA-Z+]+))(|_part-(?P<part>(mag|phase|real|imag)))_(T1w|T2w|PDw|T2starw|FLAIR|inplaneT1|inplaneT2|PDT2|angio|T2star)\.(nii.gz|nii|json)$`
+	- `.*?/sub-(?P<subject>[0-9a-zA-Z+]+)/(|ses-(?P<session>[0-9a-zA-Z+]+)/)anat/sub-(?P=subject)(|_ses-(?P=session))(|_acq-(?P<acquisition>[0-9a-zA-Z+]+))(|_ce-(?P<ceagent>[0-9a-zA-Z+]+))(|_rec-(?P<reconstruction>[0-9a-zA-Z+]+))(|_run-(?P<run>[0-9]+))(|_part-(?P<part>(mag|phase|real|imag)))_(T1w|T2w|PDw|T2starw|FLAIR|inplaneT1|inplaneT2|PDT2|angio|T2star)\.(nii.gz|nii|json)$`
 The following files were not matched by any regex schema entry:
 	* `/home/chymera/.data2/datalad/000026/noncompliant/sub-EXC022/anat/sub-EXC022_ses-MRI_flip-1_VFA.nii.gz
 The following mandatory regex schema entries did not match any files: