Install on AIX 7.2 failed

Hi,

I am trying to install gotestsum on AIX 7.2 ppc64 and get following error:

```
$ go install gotest.tools/gotestsum@latest
go: downloading gotest.tools/gotestsum v1.13.0
go: downloading gotest.tools v2.2.0+incompatible
go: downloading github.com/dnephin/pflag v1.0.7
go: downloading github.com/fatih/color v1.18.0
go: downloading github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
go: downloading golang.org/x/sync v0.17.0
go: downloading github.com/bitfield/gotestdox v0.2.2
go: downloading golang.org/x/tools v0.36.0
go: downloading golang.org/x/sys v0.36.0
go: downloading golang.org/x/term v0.35.0
go: downloading golang.org/x/text v0.17.0
go: downloading github.com/mattn/go-isatty v0.0.20
go: downloading github.com/mattn/go-colorable v0.1.13
go: downloading golang.org/x/mod v0.27.0
# gotest.tools/gotestsum/cmd
go/pkg/mod/gotest.tools/gotestsum@v1.13.0/cmd/watch.go:53:46: event.Args undefined (type filewatcher.Event has no field or method Args)
```

The golang version is the latest from AIX toolbox:
go version go1.26.5 aix/ppc64

Start at cmd/watch.go:53 and inspect how filewatcher.Event is used, then compare the dependency or API available on AIX. Re-run the reported go install command on Go 1.26.5 aix/ppc64; done means gotestsum installs without the event.Args compile error and watch mode still works.

Written by the indexing model from the issue text.