Add guard for git-sync-all for non-main branch

Only pull/push non-syncing repos (currently nixos and emacs) if on the
"main" branch, echo warning message and skip otherwise.

home/scripts/git-sync-all.sh

@@ -46,8 +46,12 @@ for i in "${!PULL_DIRS[@]}"; do
     fi
     (
         cd "$DIRECTORY" || exit
-        git remote set-url origin "$URL"
-        git pull --ff-only
-        git push
+        if [ "$(git branch --show-current)" = "main" ]; then
+            git remote set-url origin "$URL"
+            git pull --ff-only
+            git push
+        else
+            echo "Not syncing repo $DIRECTORY on branch $(git branch --show-current)"
+        fi
     )
 done