Update octicon version

[damithc]

Some of these octicons don't seem to be available (or looks different) e.g., https://primer.style/octicons/file-diff-16

Perhaps we need to update our octicon version?

[wxwxwxwx9]

Our version is indeed rather outdated 😓

[ong6]

Hi after doing some light testing, it seems the fix for this is simply running lerna add @primer/octicons packages/core not sure if this is worth a individual PR? Should I add it to my PR at #1647 ?

[wxwxwxwx9]

@ong6 Hi there! Thanks for taking a look at this.

I think it will be better if we create a new PR for this :-)

It will be more in line with the guideline set out below.

https://se-education.org/guides/guidelines/PRs.html

[ong6]

@wxwxwxwx9 Thanks for the clarification! Was not sure if a one line update warranted a PR XD