workload/schemachange: setColumnType operations will occasionally fail

Previously this test would fail due to 0A000 and 2BP01
even though those failures are expected.
In this code changes we properly handle these errors.

Epic: CRDB-25314

Fixes: cockroachdb#66662
Release note: None

pkg/workload/schemachange/operation_generator.go

@@ -2515,25 +2515,33 @@ func (og *operationGenerator) setColumnType(ctx context.Context, tx pgx.Tx) (*op
 		return nil, err
 	}
 
+	colIsRefByComputed, err := og.colIsRefByComputed(ctx, tx, tableName, columnForTypeChange.name)
+	if err != nil {
+		return nil, err
+	}
+
 	stmt := makeOpStmt(OpStmtDDL)
 	if newType != nil {
 		// Ignoring the error here intentionally, as we want to carry on with
 		// the operation and not fail it prematurely.
 		kind, _ := schemachange.ClassifyConversion(context.Background(), columnForTypeChange.typ, newType)
 		stmt.expectedExecErrors.addAll(codesWithConditions{
 			{code: pgcode.CannotCoerce, condition: kind == schemachange.ColumnConversionImpossible},
-			{code: pgcode.FeatureNotSupported, condition: kind != schemachange.ColumnConversionTrivial},
 		})
+		stmt.potentialExecErrors.add(pgcode.FeatureNotSupported)
 	}
 
 	stmt.expectedExecErrors.addAll(codesWithConditions{
 		{code: pgcode.UndefinedObject, condition: newType == nil},
-		{code: pgcode.DependentObjectsStillExist, condition: columnHasDependencies},
+		{code: pgcode.DependentObjectsStillExist, condition: columnHasDependencies || colIsRefByComputed},
 	})
 
+	stmt.potentialExecErrors.add(pgcode.DependentObjectsStillExist)
+
 	stmt.sql = fmt.Sprintf(`%s ALTER TABLE %s ALTER COLUMN %s SET DATA TYPE %s`,
 		setSessionVariableString, tableName.String(), columnForTypeChange.name.String(), newTypeName.SQLString())
 	return stmt, nil
+
 }
 
 func (og *operationGenerator) alterTableAlterPrimaryKey(

pkg/workload/schemachange/optype.go

@@ -268,7 +268,7 @@ var opWeights = []int{
 	alterTableAddColumn:               1,
 	alterTableAddConstraintForeignKey: 1,
 	alterTableAddConstraintUnique:     1,
-	alterTableAlterColumnType:         0, // Disabled and tracked with #66662.
+	alterTableAlterColumnType:         1,
 	alterTableAlterPrimaryKey:         1,
 	alterTableDropColumn:              1,
 	alterTableDropColumnDefault:       1,