Add regression test

tests/cases/compiler/substitutionTypesInIndexedAccessTypes.ts

@@ -0,0 +1,20 @@
+// @strict: true
+
+// Repro from #31086
+
+type UserArgs = {
+  select?: boolean
+};
+
+type Subset<T, U> = { [key in keyof T]: key extends keyof U ? T[key] : never };
+
+declare function withBoundary<T extends UserArgs>(args?: Subset<T, UserArgs>): T;
+declare function withoutBoundary<T extends UserArgs>(args?: T): T;
+
+const boundaryResult = withBoundary({
+  select: true,
+});
+
+const withoutBoundaryResult = withoutBoundary({
+  select: true,
+});