In #15178, we're switching hard-coded constants in tests to insta.

This issue targets updating subtrait tests (datafusion/substrait).

Examples of tests that need to be switched to insta

• datafusion/datafusion/substrait/tests/cases/consumer_integration.rs

  Lines 226 to 229 in 45ed5aa

  	"Projection: PARTSUPP.PS_PARTKEY, sum(PARTSUPP.PS_SUPPLYCOST * PARTSUPP.PS_AVAILQTY) AS value\
  	\n Sort: sum(PARTSUPP.PS_SUPPLYCOST * PARTSUPP.PS_AVAILQTY) DESC NULLS FIRST\
  	\n Filter: sum(PARTSUPP.PS_SUPPLYCOST * PARTSUPP.PS_AVAILQTY) > (<subquery>)\
  	\n Subquery:\

• datafusion/datafusion/substrait/tests/cases/roundtrip_logical_plan.rs

  Lines 457 to 462 in 45ed5aa

  	assert_expected_plan(
  	"SELECT sum(CASE WHEN a > 0 THEN 1 ELSE NULL END) FROM data",
  	"Aggregate: groupBy=[[]], aggr=[[sum(CASE WHEN data.a > Int64(0) THEN Int64(1) ELSE Int64(NULL) END) AS sum(CASE WHEN data.a > Int64(0) THEN Int64(1) ELSE NULL END)]]\
  	\n TableScan: data projection=[a]",
  	true
  	)

Check the original issue for tips on how to do the switch and examples of completed PRs.