Fix support for prerelease exits using the new .changeset/pre layout (#711)

* Fix prerelease exit mode selection

* Improve prerelease exit changeset wording

.changeset/pre.json

@@ -1,26 +1,4 @@
 {
   "mode": "pre",
-  "tag": "next",
-  "changesets": [
-    "all-cars-grin",
-    "brave-pandas-commit",
-    "bright-lions-check",
-    "calm-files-warn",
-    "chubby-geese-sink",
-    "eight-clocks-pull",
-    "eighty-doors-swim",
-    "eighty-parks-tickle",
-    "fiery-toes-vanish",
-    "git-cli-auth-header",
-    "git-cli-server-url",
-    "green-birds-push",
-    "lemon-turtles-itch",
-    "ready-mangos-boil",
-    "shaky-rings-type",
-    "shy-months-crash",
-    "silent-tips-dance",
-    "strict-hotels-laugh",
-    "tidy-bots-smile",
-    "yellow-roses-fix"
-  ]
+  "tag": "next"
 }

.changeset/quick-spoons-smile.md

@@ -0,0 +1,5 @@
+---
+"@changesets/action": patch
+---
+
+Fix support for prerelease exits using the new `.changeset/pre` layout.