Maintainer's checklist on accepting formula PR

utils/curl.rb: accept 1xx HTTP status codes

Create '.keepme' files in directories

build: bump github-pages from 198 to 200 in /docs

Bumps [github-pages](https://github.com/github/pages-gem) from 198 to 200.
- [Release notes](https://github.com/github/pages-gem/releases)
- [Commits](https://github.com/github/pages-gem/compare/v198...v200

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

RFC 2616 states:

A client MUST be prepared to accept one or more 1xx status responses
prior to a regular response, even if the client does not expect a 100
(Continue) status message. Unexpected 1xx status responses MAY be
ignored by a user agent.

In the rare cases that we encounter a formula URL with a server that
provides a preliminary 1xx status code, it seems that (at least during
audit) we are failing on encountering this status code, even though
retrieving the file will succeed without issues.

Fix `brew ruby -r`.

os/linux: add, use OS::Linux.os_version

Use AppleScript to check if GUI apps are running.

Docs: Add a link to the linuxbrew-core maintainer guide

Maintainer's guide for Homebrew on Linux (linuxbrew-core)

- There are a lot more manual steps in Homebrew on Linux (Linuxbrew)
  land than there are in Homebrew (core), it feels like.
- This is a first attempt at a maintainer's guide. I have basically
  tried to brain-dump everything that Michka and Shaun have taught me
  over the months into something consumable for future Homebrew on Linux
  maintainers!
- Some of it is overly verbose - the merging docs are taken from
  [Linuxbrew/homebrew-developer's docs](https://github.com/Linuxbrew/homebrew-developer/blob/master/docs/merge-homebrew-core.md)
  which were recently updated to reflect reality but probably don't need
  to have so many words: just some instructions. :-)

Add `GitHub::check_runs`.

Add missing `require`.

Similar to MacOS.version. A bit cleaner for us here but also plan on
using this in Homebrew/homebrew-bundle.

Skip AppleScript actions if Automation Access isn't granted.

Improve readability of `brew upgrade`

Revert "argv: move options_only to cli/args"

Revert "argv: move flags_only to cli/args"

build: bump parser from 2.6.4.0 to 2.6.4.1 in /Library/Homebrew

Bumps [parser](https://github.com/whitequark/parser) from 2.6.4.0 to 2.6.4.1.
- [Release notes](https://github.com/whitequark/parser/releases)
- [Changelog](https://github.com/whitequark/parser/blob/master/CHANGELOG.md)
- [Commits](https://github.com/whitequark/parser/compare/v2.6.4.0...v2.6.4.1

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

prof: use ruby-prof 0.18.0