Reduce subheading length to <100 characters

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What does this MR do?

@marcel.amirault, as part of tidying up subheading lengths as part of #467298, I found these in docs you're likely familiar with. I don't guarantee I made the best possible wording choices here - these pages aren't in my area of expertise - feel free to make any changes you think make for better subtitles.

For extra credit, if you see a way to fix the title of data/deprecations/15-8-deprecate-disabled-with-override-runner-setting-value.yml please send me a merge request?

Related issues

Related to Track subheading length improvements (#467298)

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