docs: gpbackup - fix typo - remove extra bracket
[<b>-exclude-table</b> <varname>schema.table</varname>]
[<b>-exclude-table-file</b> <varname>file_name</varname>]
[<b>-include-schema</b> <varname>schema_name</varname>]
- [[<b>-include-table</b> <varname>schema.table</varname>]
+ [<b>-include-table</b> <varname>schema.table</varname>]
[<b>-include-table-file</b> <varname>file_name</varname>]
[<b>-leaf-partition-data</b>]
[<b>-metadata-only</b>]
