container/initplace: return nil for createTemp error injection

This matches os package behaviour, and avoids adding the cleanup.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/dispatcher_test.go

@@ -238,8 +238,11 @@ func sliceAddr[S any](s []S) *[]S { return &s }
 
 func newCheckedFile(t *testing.T, name, wantData string, closeErr error) osFile {
 	f := &checkedOsFile{t: t, name: name, want: wantData, closeErr: closeErr}
-	// check happens in Close, and cleanup is not guaranteed to run, so relying on it for sloppy implementations will cause sporadic test results
-	f.cleanup = runtime.AddCleanup(f, func(name string) { f.t.Fatalf("checkedOsFile %s became unreachable without a call to Close", name) }, f.name)
+	// check happens in Close, and cleanup is not guaranteed to run, so relying
+	// on it for sloppy implementations will cause sporadic test results
+	f.cleanup = runtime.AddCleanup(f, func(name string) {
+		panic("checkedOsFile " + name + " became unreachable without a call to Close")
+	}, name)
 	return f
 }