Issue 1227 - Allow materialisation of df_representatives with no _ suffix

[RobinL]

Bug reported here:
#1227

The final table is called (templated name):
__splink__df_representatives
whereas intermedaite tables are called e.g.
__splink__df_representatives_1
__splink__df_representatives_2 etc.

This modifies the regex so __splink__df_representatives is also materialised

[github-actions]

Test: test_2_rounds_1k_duckdb

Percentage change: -16.0%

	date	time	stats_mean	stats_min	commit_info_branch	commit_info_id	machine_info_cpu_brand_raw	machine_info_cpu_hz_actual_friendly	commit_hash
849	2022-07-12	18:40:05	1.89098	1.87463	splink3	c334bb9	Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz	2.7934 GHz	c334bb9
1617	2023-05-10	12:03:49	1.6375	1.57496	(detached head)	52544b3	Intel(R) Xeon(R) Platinum 8171M CPU @ 2.60GHz	2.0951 GHz	52544b3

Test: test_2_rounds_1k_sqlite

Percentage change: -9.5%

	date	time	stats_mean	stats_min	commit_info_branch	commit_info_id	machine_info_cpu_brand_raw	machine_info_cpu_hz_actual_friendly	commit_hash
851	2022-07-12	18:40:05	4.32179	4.25898	splink3	c334bb9	Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz	2.7934 GHz	c334bb9
1619	2023-05-10	12:03:49	3.87473	3.85272	(detached head)	52544b3	Intel(R) Xeon(R) Platinum 8171M CPU @ 2.60GHz	2.0951 GHz	52544b3

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