Add a CI spell check job for changed files on PRs

[jochem-brouwer]

This PR adds a CI job which will run a cspell check on only the changed files (as compared to master).

As a proof of concept and to show how spell fails (and false positives) should be fixed I've included two files.

Some notes:

• The "bonus" we get when we merge this PR is that typo-PRs will thus now also get ran through the cspell check 😄 👍
• The check runs in case sensitivity, for instance adding "Beiko" to known words will flag "beiko"
• I've added area-specific words to the global word list, like EIP, Holesky, etc.
• To add known words to a markdown file add a "comment" using [//] # cSpell:words WORD_LIST, see: https://stackoverflow.com/a/20885980
• In the Attendees section of the Meeting, wrap this in (names are obv. flagged as "spell error"):

### Attendees
[//] # cSpell:disable
* <Attendee name 1>
* <Attendee name 2>
...
* <Attendee name N>
[//] # cSpell:enable

Note: cspell defaults to US English which is why "standardisation" is flagged on Meeting-202.

Obviously open for discussion, but I think for now a spell check job on new files would be handy. On meeting-202 it found one obvious error: eaps -> EIPs. Have not checked the other files (besides throwing them in the cspell job, this obviously flags a lot of errors)

[jochem-brouwer]

Hmm ok I had assumed that some warning would pop up that PR-triggered actions are not triggered here, but it seems not. The action does run on my forked repo though: jochem-brouwer#2