Update integration_number datatype in "group" schema

[stscijgbot-jp]

Issue JP-3558 was created on JIRA by Howard Bushouse:

In the stdatamodels group.schema.yaml module, which defines the tabular data stored in the GROUP extension of data products the integration_number column is defined as int16, but it should be int32, in order to prevent values from wrapping around the limit of the int16 range.