ci: Rebase during publish step (#7229)

#### Problem

Sometimes, while the publish workflow is running, we merge a different
PR, which means that the workflow is running against an older commit.
This makes the step to push the tag commit fail sometimes, but this
happens *after* the new crate has already been published. This means
that we end up publishing crates that don't have any commits attached to
them.

#### Summary of changes

Add a step to rebase before publishing.

Author: joncinque

.github/workflows/publish-rust.yml

@@ -183,6 +183,9 @@ jobs:
           git config --global user.email "41898282+github-actions[bot]@users.noreply.github.com"
           git config --global user.name "github-actions[bot]"
 
+      - name: Rebase
+        run: git pull --rebase origin
+
       - name: Publish Crate
         id: publish
         env: