ci: rebase with --autostash on the flasher push retry

A plain `git rebase` refuses to run when the checkout has unstaged changes, so
the retry path could fail instead of retrying. The beta workflow stages a scoped
subset on purpose (production's files must never ride along), which leaves the
rest of the checkout dirty and hits this exactly; keep all three flasher pushes
identical so it cannot resurface here either. Unstaged content stays unstaged,
so nothing extra gets published.

.github/workflows/build-observer-firmwares.yml

@@ -320,7 +320,9 @@ jobs:
             fi
             echo "push rejected (attempt $attempt); rebasing onto origin/$br"
             git fetch origin "$br"
-            git rebase "origin/$br" || {
+            # --autostash so a dirty tree can never make the rebase refuse to run;
+            # nothing unstaged gets published either way.
+            git rebase --autostash "origin/$br" || {
               git rebase --abort || true
               echo "::error::flasher rebase conflicted; re-run this workflow to republish"
               exit 1

.github/workflows/sync-flasher-content.yml

@@ -86,7 +86,9 @@ jobs:
             fi
             echo "push rejected (attempt $attempt); rebasing onto origin/$br"
             git fetch origin "$br"
-            git rebase "origin/$br" || {
+            # --autostash so a dirty tree can never make the rebase refuse to run;
+            # nothing unstaged gets published either way.
+            git rebase --autostash "origin/$br" || {
               git rebase --abort || true
               echo "::error::flasher rebase conflicted; re-run this workflow to resync"
               exit 1