Improve wording under Tone of Voice

Why is this change being made?

I couldn't help noticing that the current wording ("irreverent") is a synonym (Oxford) for "disrespectful"... I'm not entirely sure whether we wanted to say "reverent" or "reverential" instead but I propose "conscientious". "Reverent" would work too although it bears a slightly different meaning.

Author Checklist

• Correct MR template applied (e.g blog post)
• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.

For help with failing pipelines reach out in #mr-buddies in Slack