fix: prevent packages that haven't been published from failing (#9169)

Simple change that will let us run `yarn run publish` even if packages don't exist.

scripts/get-unowned-packages/index.js

@@ -3,11 +3,13 @@ const PackageGraph = require(`@lerna/package-graph`)
 const filterPackages = require(`@lerna/filter-packages`)
 const util = require(`util`)
 const path = require(`path`)
-const exec = util.promisify(require(`child_process`).exec)
+const { exec, execSync } = require(`child_process`)
+
+const execP = util.promisify(exec)
 
 const getPackagesWithReadWriteAccess = async user => {
   const cmd = `npm access ls-packages ${user}`
-  const { stdout } = await exec(cmd)
+  const { stdout } = await execP(cmd)
   const permissions = JSON.parse(stdout)
   return Object.entries(permissions).reduce((lookup, [pkgName, access]) => {
     if (access === `read-write`) {
@@ -36,15 +38,26 @@ module.exports = function getUnownedPackages({
     // infer user from npm whoami
     // set registry because yarn run hijacks registry
     if (!user) {
-      user = await exec(`npm whoami --registry https://registry.npmjs.org`)
+      user = await execP(`npm whoami --registry https://registry.npmjs.org`)
         .then(({ stdout }) => stdout.trim())
         .catch(() => process.exit(1))
     }
 
     const alreadyOwnedPackages = await getPackagesWithReadWriteAccess(user)
 
     const publicGatsbyPackagesWithoutAccess = publicGatsbyPackages.filter(
-      pkg => !alreadyOwnedPackages[pkg.name]
+      pkg => {
+        if (alreadyOwnedPackages[pkg.name]) {
+          return false
+        }
+
+        try {
+          return !execSync(`npm view ${pkg.name} version`, { stdio: `pipe` })
+            .stderr
+        } catch (e) {
+          return false
+        }
+      }
     )
 
     return {