fix: incorrect index in TypeEqual for ConstraintType (#2754)

Just a typo.

Closes #2727

explorer/ast/value.cpp

@@ -832,7 +832,7 @@ auto TypeEqual(Nonnull<const Value*> t1, Nonnull<const Value*> t2,
           return false;
         }
         for (size_t j = 0; j < equality1.values.size(); ++j) {
-          if (!ValueEqual(equality1.values[i], equality2.values[i],
+          if (!ValueEqual(equality1.values[j], equality2.values[j],
                           equality_ctx)) {
             return false;
           }

explorer/testdata/constraint/where_multiple_equality.carbon

@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface IFace {}
+
+impl {.IFace : (type where type == i32 and type == i32 and type == i32, )} as IFace {
+}
+
+fn Main() -> i32 {
+  return 0;
+}