build: fix FUSE mount test failures on GitHub actions runners

Runner image ubuntu24/20260726.254 updated podman from 4.9.3 to 5.8.4
which is installed from the podman-static bundle. This bundle ships a
non-setuid fusermount3 in /usr/local/bin which shadows the setuid
/usr/bin/fusermount3 from the fuse3 package (as /usr/local/bin comes
first in PATH). A non-setuid fusermount3 cannot mount as an
unprivileged user, so the cmd/mount and cmd/mount2 tests failed with:

    fusermount3: mount failed: Operation not permitted

Fix by removing the podman bundled fusermount binaries so the distro
provided setuid one is used.

.github/workflows/build.yml

@@ -165,6 +165,11 @@ jobs:
           sudo chown root:$USER /etc/fuse.conf
           sudo apt-get update
           sudo apt-get install -y fuse3 libfuse-dev rpm pkg-config git-annex git-annex-remote-rclone nfs-common
+          # The podman static bundle in runner image ubuntu24/20260726.254 and
+          # later ships a non-setuid fusermount3 in /usr/local/bin which
+          # shadows the setuid one from the fuse3 package and breaks FUSE
+          # mounts with "Operation not permitted", so remove it.
+          sudo rm -f /usr/local/bin/fusermount /usr/local/bin/fusermount3
         if: matrix.os == 'ubuntu-latest'
 
       - name: Install Libraries on macOS