[infra] use npx to run auto (#1521)

The canary release failed due to not finding auto:
https://github.com/tldraw/tldraw/actions/runs/5178225013/jobs/9329393446

No idea why, but I'm going to try running it with npx here.

scripts/publish-canary.ts

@@ -18,7 +18,11 @@ async function main() {
 	}
 
 	// module was called directly
-	const bumpType = (await exec('auto', ['version'])).trim() as 'major' | 'minor' | 'patch' | ''
+	const bumpType = (await exec('npx', ['auto', 'version'])).trim() as
+		| 'major'
+		| 'minor'
+		| 'patch'
+		| ''
 
 	nicelog('bumpType', bumpType)
 	if (bumpType === '') {