Fix some minor formatting typos in associations docs

[braingram]

While looking through the associations docs I found a few minor formatting typos.

overview misconfigured code-block:

• before: https://jwst-pipeline.readthedocs.io/en/latest/jwst/associations/overview.html#usage
• after: https://jwst-pipeline--7694.org.readthedocs.build/en/7694/jwst/associations/overview.html#usage

misconfigured doctest-skip:

• before: https://jwst-pipeline.readthedocs.io/en/latest/jwst/associations/association_reference.html#rule-registration
• after: https://jwst-pipeline--7694.org.readthedocs.build/en/7694/jwst/associations/association_reference.html#rule-registration

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (b79a88a) 76.56% compared to head (073b544) 76.56%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7694   +/-   ##
=======================================
  Coverage   76.56%   76.56%           
=======================================
  Files         456      456           
  Lines       36877    36877           
=======================================
  Hits        28234    28234           
  Misses       8643     8643           

Flag	Coverage Δ		*Carryforward flag
nightly	77.43% <ø> (ø)		Carriedforward from b79a88a

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[hbushouse]

Looks good. Thanks for the fixes.