docs: fix typos

[pjonsson]

Reason for this pull request

Fix typos in the docs.

Proposed changes

• Closes #xxxx
• Tests added / passed
• Fully documented, including docs/about/whats_new.rst for all changes

[SpacemanPaul]

Thanks Peter.

Happy to merge this, but could you please:

1. Combine the change in configuration.rst: align comment and code #1578 into this PR; and
2. Add a line to the "1.9.next" section of docs/about/whats_new.rst describing the PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.80%. Comparing base (93e1d01) to head (44fe10c).

❗ Current head 44fe10c differs from pull request most recent head b8856f2. Consider uploading reports for the commit b8856f2 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##           develop-1.9    #1577   +/-   ##
============================================
  Coverage        85.80%   85.80%           
============================================
  Files              140      140           
  Lines            15402    15402           
============================================
  Hits             13215    13215           
  Misses            2187     2187           

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[SpacemanPaul]

See comment above - please combine with your other documentation PR and add a line to doc/about/whats_new.rst

[SpacemanPaul]

Thanks Peter!