fix: Checkout master before hogql-diff and use new GH syntax

[tomasfarias]

Problem

I'm seeing a fatal: bad revision 'master' line when checking if hogql-parser has changed compared to master. This is causing PRs to run for 5-7 minutes setting-up hogql/antlr, even if nothing changed.

The solution should be to fetch origin and diff with origin/master. I'm doing this manually which is probably not the cleanest, but given the amount of time lost to building antlr, this is nothing.

Moreover, we are using the set-output command which was deprecated last year, but then un-deprecated this year.

It's not clear to me whether ::set-otuput is still supported or not, but anyways, we should use the new recommended syntax.

Changes

• Swap echo "::set-output name=changed::$changed" for echo "changed=$changed" >> $GITHUB_OUTPUT
• Fetch origin and diff against origin/master for hogl changes.

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

How did you test this code?

I rebased my PR on top of this, notice no time spent building antlr: https://github.com/PostHog/posthog/actions/runs/6789574178/job/18457089273?pr=18463. Compare that run against another earlier PR I merged which did built antlr: https://github.com/PostHog/posthog/actions/runs/6782379713/job/18435144400. None of them changed hogql_parser in anyway.

Logs of the old run:

Run changed=$(git diff --quiet HEAD master -- hogql_parser/ && echo "false" || echo "true")
fatal: bad revision 'master'
Warning: The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

[tomasfarias]

If you see test failures with a missing libantlr requirement, you just gotta blow up the virtualenv cache.