Fix 1.18 linting

[liam-lloyd]

No description provided.

[liam-lloyd]

This is a weird PR and Github isn't presenting it correctly. Here's what's actually going on:

• When we updated Archivematica to 1.18, there seems to have been an error in RELEASENOTES.md, or perhaps we made a mistake in the rebase, that has caused our linting to fail ever since
• This commit re-does the rebase against upstream's stable/1.18.x, which picks up changes to RELEASENOTES.md that fix the linting errors. This is the only actual difference between this branch and main.
• You can verify the actual changes here by running git diff main fix_1.18_linting and by running make test-linting from the hack directory locally.
• When this is approved, rather than merging it I will force push this branch to main to replace main with this more correct copy of our changes on top of upstream's 1.18 branch.

[cecilia-donnelly]

Just a note that the change to fix the isInstance call and add tests are now in main as well and not on this branch.

[cecilia-donnelly]

It is weird that GitHub can't figure this out, but I did verify the changes from the command line. It looks like you'll need to rebase on our main to pick up the fix to isInstance you just made, or cherry-pick it over.