CI: go back to macos-latest

Now that it seems we found a fix to #200, there is no reason to stick
to macos-11, which will likely be deprecated soon.

Update actions/setup-go to its latest version as well.
The new version uses caching by default, which we do not need.

While here, tidy up the cloneFile docs a bit.

.github/workflows/test.yml

@@ -15,16 +15,17 @@ jobs:
         - '1.20.x'
         os:
         - ubuntu-latest
-        - macos-11
+        - macos-latest
         - windows-latest
     runs-on: ${{ matrix.os }}
     steps:
     - name: Checkout code
       uses: actions/checkout@v3
     - name: Install Go
-      uses: actions/setup-go@v3
+      uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.go-version }}
+        cache: false # our tests are quick enough
     - name: Test
       run: |
         go test ./...

clonefile.go

@@ -5,7 +5,7 @@ package testscript
 
 import "os"
 
-// cloneFile creates to as a hard link to the from file.
+// cloneFile makes a clone of a file via a hard link.
 func cloneFile(from, to string) error {
 	return os.Link(from, to)
 }

clonefile_darwin.go

@@ -2,7 +2,7 @@ package testscript
 
 import "golang.org/x/sys/unix"
 
-// cloneFile clones the file from to the file to.
+// cloneFile makes a clone of a file via MacOS's `clonefile` syscall.
 func cloneFile(from, to string) error {
 	return unix.Clonefile(from, to, 0)
 }

clonefile_other.go

@@ -5,7 +5,9 @@ package testscript
 
 import "fmt"
 
-// We don't want to use hard links on Windows, as that can lead to "access denied" errors when removing.
+// cloneFile does not attempt anything on Windows, as hard links on it have
+// led to "access denied" errors when deleting files at the end of a test.
+// We haven't tested platforms like plan9 or wasm/wasi.
 func cloneFile(from, to string) error {
 	return fmt.Errorf("unavailable")
 }

exe.go

@@ -117,10 +117,9 @@ func RunMain(m TestingM, commands map[string]func() int) (exitCode int) {
 // Second, symlinks might not be available on some environments, so we have to
 // implement a "full copy" fallback anyway.
 //
-// However, we do try to use a hard link, since that will probably work on most
+// However, we do try to use cloneFile, since that will probably work on most
 // unix-like setups. Note that "go test" also places test binaries in the
-// system's temporary directory, like we do. We don't use hard links on Windows,
-// as that can lead to "access denied" errors when removing.
+// system's temporary directory, like we do.
 func copyBinary(from, to string) error {
 	if err := cloneFile(from, to); err == nil {
 		return nil