Replaces a number of error equality checks with errors.Is

Signed-off-by: redwrasse <mail@redwrasse.io>

client/pkg/fileutil/lock_flock.go

@@ -17,6 +17,7 @@
 package fileutil
 
 import (
+	"errors"
 	"os"
 	"syscall"
 )
@@ -28,7 +29,7 @@ func flockTryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, err
 	}
 	if err = syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
 		f.Close()
-		if err == syscall.EWOULDBLOCK {
+		if errors.Is(err, syscall.EWOULDBLOCK) {
 			err = ErrLocked
 		}
 		return nil, err