docs: Fix a few typos

[timgates42]

There are small typos in:

• docs/job_definition.rst
• docs/run_types.rst
• plan/job.py

Fixes:

• Should read separate rather than seperate.
• Should read insensitive rather than insenstive.
• Should read should rather than shoud.
• Should read separated rather than seperated.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md