Apply suggestions from code review

Co-authored-by: Marco Ieni <[email protected]>

Author: the8472

src/ci/scripts/free-disk-space-linux.sh

@@ -260,7 +260,8 @@ checkAlternative() {
     # ignore-tidy-linelength
     local mntopts="defaults,discard,journal_async_commit,barrier=0,noauto_da_alloc,lazytime,data=writeback"
 
-    # GHA has a 2nd disk mounted at /mnt that is almost empty
+    # GHA has a 2nd disk mounted at /mnt that is almost empty.
+    # Check if it's a valid mountpoint and it has enough available space.
     if mountpoint /mnt && [ "$available_space_kb" -ge "$space_target_kb" ]; then
         local blkdev=$(df -k "$mountpoint" --output=source | tail -n 1)
         echo "Sufficient space available on $blkdev mounted at $mountpoint"
@@ -271,6 +272,8 @@ checkAlternative() {
         sudo mount $blkdev ./obj -o $mntopts || sudo dmesg | tail -n 20
         sudo chown -R "$USER":"$USER" ./obj
 
+        # Exit from this script to avoid wasting time removing disk space,
+        # as we already have enough disk space in the alternative drive.
         exit 0
     fi