vendor-install: Update aarch64 and add armv6

zip: overwrite existing files

Fix RuboCop namespace.

Add `GitHub::create_check_run` function.

bottle: don't keep old cellar

Co-Authored-By: Mike McQuaid <mike@mikemcquaid.com>

completions/zsh: add --greedy argument for `brew cask outdated`

Deal with GMake Makefile conditional assignment operators.

[Interesting Taps and Forks] Update unmaintained ffmpeg tap to Current

Ordinarily variable assignments in Makefiles are done simply with an
unconditional assignment: the equals sign.  There are variants of this:

FOO := $(BAR)	Avoid recursively expand variables.
FOO ?= bar	Assign only if $(FOO) is not already set.
FOO += bar	Add more to a variable.
FOO != bar	Execute a shell script and assign result to $(FOO).

See also
https://www.gnu.org/software/make/manual/html_node/Conditional-Example.html
https://www.gnu.org/software/make/manual/html_node/Flavors.html

brew test: more fixes for ARM

On ARMv7, the arch name is armv7l instead of armv7. So update the bottle
file name accordingly.

brew tests: fix for ARM

This ensures correct RUBY_PATH is used when running `brew tests` with
custom `HOMEBREW_RUBY_PATH`

More info: https://github.com/Homebrew/brew/pull/6617#discussion_r336431131

Fix `shellenv` when using `-u`.

doctor: list any uncommitted modified files in CI

Also fix the absolute link used by testball_bottle-0.1.intel_macintosh.bottle.tar.gz

Fix `#match?` on `nil`.

os/mac/xcode: fallback to clang version for detecting CLT.

For some reason `pkgutil --pkgs` no longer lists the CLT after the
Catalina supplemental update.

Fixes https://github.com/Homebrew/brew/issues/6610

vendor-install: Add ruby bottle for aarch64

bottle: do not install patchelf if --skip-relocation flag is passed

Skip quarantining symlinks.

Fix missing `command` method.

README: update maintainers.