dev: fix commit linter target and lint all commits

- Was formerly processing the internal merge commit, which never conforms
  to our conventions, but is also unrelated to the work at hand.
- Now lints the range of commits applicable to the event, and not just
  the latest commit.

.github/workflows/lint.yml

@@ -11,4 +11,4 @@ jobs:
       - uses: actions/checkout@v2.3.1
         with:
           fetch-depth: 0
-      - run: bin/doom ci lint-commits HEAD~1
+      - run: bin/doom ci lint-commits ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }}

core/cli/ci.el

@@ -144,7 +144,7 @@
       (insert
        (cdr (doom-call-process
              "git" "log"
-             (format "%s...%s" from (or to "HEAD")))))
+             (format "%s..%s" from (or to "HEAD")))))
       (while (re-search-backward "^commit \\([a-z0-9]\\{40\\}\\)" nil t)
         (push (cons (match-string 1)
                     (replace-regexp-in-string