Add changeset script

Allows us to run `pnpm run changeset`, which is more standardised across
packages managers.

https://github.com/antfu/ni#nr---run

.github/workflows/validate.yml

@@ -64,7 +64,7 @@ jobs:
 
       - if: github.event_name == 'push'
         name: Dry-run changelog versioning
-        run: pnpm exec changeset version
+        run: pnpm run changeset version
 
       - if: github.event_name == 'push'
         name: Dry-run site packaging

CONTRIBUTING.md

@@ -189,7 +189,7 @@ a changeset is not necessary for:
 - [npm dev dependencies](https://github.com/seek-oss/skuba/blob/master/package.json)
 
 ```shell
-pnpm exec changeset
+pnpm run changeset
 ```
 
 The Changesets CLI is interactive and follows [semantic versioning]:

package.json

@@ -29,6 +29,7 @@
   ],
   "scripts": {
     "build": "scripts/build.sh",
+    "changeset": "changeset",
     "deploy": "scripts/deploy.sh",
     "format": "pnpm run --silent skuba format",
     "lint": "pnpm run --silent skuba lint && pnpm run --silent lint:md",