Switch publish workflow to use the beta SDK

This is needed because the ffigen package depends on the beta
version of the SDK.

.github/workflows/publish.yaml

diff --git a/.github/workflows/publish.yaml b/.github/workflows/publish.yaml
index 4bac353..4c00b14 100644
--- a/.github/workflows/publish.yaml
+++ b/.github/workflows/publish.yaml
@@ -17,3 +17,4 @@
       pull-requests: write # Required for writing the pull request note
     with:
       write-comments: false
+      sdk: beta