Update all dependencies of WCFS to their recent versions:

- go-fuse: update to pick up https://github.com/hanwen/go-fuse/commit/265a3926
  and https://github.com/hanwen/go-fuse/commit/90b055af. The first patch
  potentially improves performance, while the second fixes support for
  neo:// with multiple masters.
- go123: add support for go1.20
- testify: some bugfixes (we use this package only during tests)

The following dependencies were not updated by upstream at all:

- glog
- overflow
- ogórek
- pkg/errors

.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/wendelin.core!16