fix: detect correct "locked by others" error on windows

Also use the newer "errors.Is" where possible.

Author: Stebalien

Diff for: fslock.go

@@ -42,7 +42,7 @@ func Lock(confdir, lockFileName string) (io.Closer, error) {
 				Path: lockFilePath,
 				Err:  LockedError("lock is already held by us"),
 			}
-		case os.IsPermission(err) || isLockCreatePermFail(err):
+		case errors.Is(err, os.ErrPermission) || isLockCreatePermFail(err):
 			// lock fails on permissions error
 
 			// Using a path error like this ensures that

Diff for: fslock_posix.go

@@ -3,10 +3,27 @@
 package fslock
 
 import (
+	"errors"
 	"strings"
 	"syscall"
 )
 
+var lockedMsgs = []string{
+	// unix
+	"resource temporarily unavailable",
+	// linux
+	"cannot access the file because it is being used by another process",
+}
+
 func lockedByOthers(err error) bool {
-	return err == syscall.EAGAIN || strings.Contains(err.Error(), "resource temporarily unavailable")
+	if errors.Is(err, syscall.EAGAIN) {
+		return true
+	}
+	msg := err.Error()
+	for _, target := range lockedMsgs {
+		if strings.Contains(msg, target) {
+			return true
+		}
+	}
+	return false
 }

Diff for: fslock_test.go

@@ -153,7 +153,7 @@ func TestLockedByOthers(t *testing.T) {
 	}
 	pe, ok := err.(*os.PathError)
 	if !ok {
-		t.Fatalf("wrong error type %T", err)
+		t.Fatalf("wrong error type %T: %s", err, err)
 	}
 	if got := pe.Error(); !strings.Contains(got, wantErr) {
 		t.Fatalf("error %q does not contain %q", got, wantErr)