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

This issue targets updating optimizer tests (datafusion/optimizer).

Examples of tests that need to be switched to insta

• datafusion/datafusion/optimizer/tests/optimizer_integration.rs

  Lines 115 to 117 in 49737d8

  	let expected = "Repartition: DistributeBy(test.col_utf8)\
  	\n TableScan: test projection=[col_int32, col_utf8]";
  	assert_eq!(expected, format!("{plan}"));

• datafusion/datafusion/optimizer/src/optimize_projections/mod.rs

  Lines 1069 to 1071 in 49737d8

  	\n Projection: \
  	\n Aggregate: groupBy=[[]], aggr=[[count(Int32(1))]]\
  	\n TableScan: ?table? projection=[]";

• datafusion/datafusion/optimizer/src/decorrelate_predicate_subquery.rs

  Lines 465 to 473 in 49737d8

  	\n LeftSemi Join: Filter: test.b = __correlated_sq_2.c [a:UInt32, b:UInt32, c:UInt32]\
  	\n LeftSemi Join: Filter: test.c = __correlated_sq_1.c [a:UInt32, b:UInt32, c:UInt32]\
  	\n TableScan: test [a:UInt32, b:UInt32, c:UInt32]\
  	\n SubqueryAlias: __correlated_sq_1 [c:UInt32]\
  	\n Projection: sq_1.c [c:UInt32]\
  	\n TableScan: sq_1 [a:UInt32, b:UInt32, c:UInt32]\
  	\n SubqueryAlias: __correlated_sq_2 [c:UInt32]\
  	\n Projection: sq_2.c [c:UInt32]\
  	\n TableScan: sq_2 [a:UInt32, b:UInt32, c:UInt32]";

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