chore: Update reservedTableColumns variable

[kurokirasama]

• Updated the reservedTableColumns variable to 5.
• This change reflects the updated spreadsheet structure.

I think that the spreadsheet with columns

Playlist ID	
Last Update (Timestamp)	
Frequency (hours)	
Delete (days)	
<--	
Channel IDs [OR] Channel Names [OR] Playlist IDs [OR] Special Keyword (i.e. "ALL" for all subscribed channels)																							

Is the latest one, not the one in the Readme. If so, then there was an error in the index of the mentioned column.

[victorjzsun]

There was a recent addition of a Shorts column bringing the Channels column to column G aka index 6