[PATCH] backup: Fix trivial typo and error message issues

Hi all,

I noticed two trivial issues in backup-related code:
1. backup_manifest.c: The timeline mismatch error message uses `starttli` instead of `endtli`.
2. basebackup_copy.c: There is a spelling error (sine → since) in the comment above the `PROGRESS_REPORT_BYTE_INTERVAL` macro.

```
--- a/src/backend/backup/backup_manifest.c
+++ b/src/backend/backup/backup_manifest.c
@@ -253,7 +253,7 @@ AddWALInfoToBackupManifest(backup_manifest_info *manifest, XLogRecPtr startptr,
                if (first_wal_range && endtli != entry->tli)
                        ereport(ERROR,
                                        errmsg("expected end timeline %u but found timeline %u",
-                                                  starttli, entry->tli));
+                                                  endtli, entry->tli));
```

```
- * So we only check it after the number of bytes sine the last check reaches
+ * So we only check it after the number of bytes since the last check reaches
```

--
Regards,
Man Zeng
www.openhalo.org