ci: Improve GitHub Action modularity (#18861)

- Closes: https://github.com/zed-industries/zed/issues/19351
- Switch to using the official [typos GitHub Action](https://github.com/crate-ci/typos/blob/master/docs/github-action.md)
- Move the typos check into `actions/check_style`
- Move Squawk Postgres migration check out of `actions/check_style` file into ci.yml
- `actions/check_style` can now be run on stateless/linux runners (previous required self-hosted MacOS runner)
- ci.yml: Split old `style` into checks into those that can run statelessly (linux) and everything else into a new `migration` group which benefit from the full git checkout available on the MacOS runners.
- ci.yml: Move `Check unused dependencies` from style to `linux_tests`
- Add `if: github.repository_owner == 'zed-industries'` to all jobs so they won't try and run on GitHub forks.

script/check-spelling

@@ -1,14 +0,0 @@
-#!/bin/sh
-
-set -eu
-
-TYPOS_CLI_VERSION=1.24.6
-TARGET_DIR=${1:-""}
-
-if ! cargo install --list | grep "typos-cli v$TYPOS_CLI_VERSION" > /dev/null; then
-    echo "Installing typos-cli@$TYPOS_CLI_VERSION..."
-    cargo install "typos-cli@$TYPOS_CLI_VERSION"
-else
-    echo "typos-cli@$TYPOS_CLI_VERSION is already installed."
-fi
-typos $TARGET_DIR