Reduce file permissions in y.go (#1056)

one of the issues listed in
https://deepsource.io/gh/jaipradeesh/badger/issues/ is excessive
permissions. The functions in y.go are opening files with 0666
permissions. This PR changes them to 0600 for improved security.

y/y.go

@@ -75,7 +75,7 @@ func CreateSyncedFile(filename string, sync bool) (*os.File, error) {
 	if sync {
 		flags |= datasyncFileFlag
 	}
-	return os.OpenFile(filename, flags, 0666)
+	return os.OpenFile(filename, flags, 0600)
 }
 
 // OpenSyncedFile creates the file if one doesn't exist.
@@ -84,7 +84,7 @@ func OpenSyncedFile(filename string, sync bool) (*os.File, error) {
 	if sync {
 		flags |= datasyncFileFlag
 	}
-	return os.OpenFile(filename, flags, 0666)
+	return os.OpenFile(filename, flags, 0600)
 }
 
 // OpenTruncFile opens the file with O_RDWR | O_CREATE | O_TRUNC
@@ -93,7 +93,7 @@ func OpenTruncFile(filename string, sync bool) (*os.File, error) {
 	if sync {
 		flags |= datasyncFileFlag
 	}
-	return os.OpenFile(filename, flags, 0666)
+	return os.OpenFile(filename, flags, 0600)
 }
 
 // SafeCopy does append(a[:0], src...).