update cmd/gofmt source with Go 1.20

There are no relevant changes. We can start using `any`, though.

README.md

@@ -7,15 +7,15 @@
 Enforce a stricter format than `gofmt`, while being backwards compatible.
 That is, `gofumpt` is happy with a subset of the formats that `gofmt` is happy with.
 
-The tool is a fork of `gofmt` as of Go 1.19, and requires Go 1.19 or later.
+The tool is a fork of `gofmt` as of Go 1.20, and requires Go 1.19 or later.
 It can be used as a drop-in replacement to format your Go code,
 and running `gofmt` after `gofumpt` should produce no changes.
 For example:
 
 	gofumpt -l -w .
 
 Some of the Go source files in this repository belong to the Go project.
-The project includes copies of `go/printer` and `go/doc/comment` as of Go 1.19
+The project includes copies of `go/printer` and `go/doc/comment` as of Go 1.20
 to ensure consistent formatting independent of what Go version is being used.
 The [added formatting rules](#Added-rules) are implemented in the `format` package.
 

gofmt.go

@@ -239,7 +239,7 @@ func (r *reporter) getState() *reporterState {
 
 // Warnf emits a warning message to the reporter's error stream,
 // without changing its exit code.
-func (r *reporter) Warnf(format string, args ...interface{}) {
+func (r *reporter) Warnf(format string, args ...any) {
 	fmt.Fprintf(r.getState().err, format, args...)
 }
 
@@ -542,7 +542,7 @@ type module struct {
 	}
 }
 
-func loadModuleInfo(dir string) interface{} {
+func loadModuleInfo(dir string) any {
 	cmd := exec.Command("go", "mod", "edit", "-json")
 	cmd.Dir = dir