Non-unicode in /proc/mounts

Upgrade crashes with `UnicodeDecodeError`: ``` Traceback (most recent call last): File "/usr/lib/linuxmint/mintupgrade/checks.py", line 94, in run self.do_run() File "/usr/lib/linuxmint/mintupgrade/checks.py", line 697, in do_run self.check_disk_space_requirements(cache) File "/usr/lib/linuxmint/mintupgrade/checks.py", line 741, in check_disk_space_requirements for line in mounts: File "<frozen codecs>", line 322, in decode UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb1 in position 1557: invalid start byte ``` Relevant code fragment (line 741): ```python with open("/proc/mounts") as mounts: for line in mounts: try: (what, where, fs, options, a, b) = line.split() except ValueError as e: continue if not where in mounted: mounted.append(where) ``` I found that my `/proc/mounts` contains a line like this: `0xB1екапируемый:0xBDебекапируемый /home/user fuse.mergerfs rw,rel… 0 0`, where `0xB1` and `0xBD` are raw bytes. Obviously, this is a mergerfs issue, but I decided to report it here anyway. ### Versions * mintupgrade: 2024.07.27.3 * mergerfs: 2.33.5-1ubuntu2