Use plistlib's load and dump instead of readPlist and writePlist.
Use plistlib's load and dump instead of readPlist and writePlist.

* fixes the error of CI for macOS on GitHub.

PiperOrigin-RevId: 448765339

google/mozc,google/mozc,fcitx/mozc,google/mozc,fcitx/mozc,fcitx/mozc,google/mozc,google/mozc,fcitx/mozc,fcitx/mozc