ci: rename the lowest job to floors and skip it on scheduled runs

[lesnik512]

This PR skips the floors job on scheduled runs with if: github.event_name != 'schedule'. The job still gates every pull request and every push to main.

It also renames the job from lowest to floors, the name the standard uses (modern-python/.github#111).

Why, per section 7 of the standard (modern-python/.github#113): direct dependencies sit at their declared floors, which don't change between runs. So a scheduled floors run can only catch transitive drift, and the scheduled pytest already covers newest-version breakage. A reusable workflow sees its caller's github context, so the callers don't change.

[github-actions]

Benchmark gate

✅ gate passed

scenario	msg/s	delete/msg	WALrec/msg	WALB/msg	fpi	upd	del	dead_tup
consumer/w1/b10	1046	1.000	6.78	914	242	5000	5000	10000
consumer/w1/b100	1291	1.000	6.83	918	243	5000	5000	10000
consumer/w2/b10	1386	1.000	6.79	960	242	5000	5000	10000
consumer/w2/b100	1652	1.000	6.73	956	243	5000	5000	10000
consumer/w4/b10	844	1.000	6.78	977	261	5000	5000	10000
consumer/w4/b100	1537	1.000	6.86	1037	244	5000	5000	10000
consumer/w1/b100/tfbs100	8517	0.010	6.07	1116	243	5000	5000	10000
producer/w1/b100	3093	0.000	3.04	584	0	0	0	0

Gated (fails the build): delete_calls + tuple counters (upd/del/ins) + the producer's insert_calls, exact; select_calls within +2; wal_records within a 10% band. msg/s, WAL bytes and total calls are informational (timing/FPI noise).