wpcom sync: Add missing push

`gh pr create` can't non-interactively push a branch and create a PR.
Just use a plain old `git push` before running `gh pr create --head`
which will work non-interactively if the branch is already pushed.

theme-utils.mjs

@@ -1041,6 +1041,7 @@ async function createGithubPR(commitMessage) {
 		git checkout -b deploy
 		git add --all
 		git commit -m "${commitMessage}"
+		git push origin deploy
 		gh pr create --fill --head deploy
 	`, true);