Parsing new expression uses incorrect variable when multiple are available

[SamirDroubi]

======================================== FAILURES =========================================
_______________________________ test_new_expression_parsing _______________________________

    def test_new_expression_parsing():
        @proc
        def bar(n: size, arr: R[n] @ DRAM):
            for i in seq(0, n):
                tmp: R
                tmp = 1.0
                arr[i] = tmp
            i: R
            i = 1.0

>       expand_dim(
            bar, "tmp : _", "n", "i"
        )

tests/test_schedules.py:1604:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
src/exo/API_scheduling.py:101: in __call__
    return self.func(*bound_args.args, **bound_args.kwargs)
src/exo/API_scheduling.py:1147: in expand_dim
    CheckEffects(new_proc_c._loopir_proc)
src/exo/effectcheck.py:537: in __init__
    body_eff = self.map_stmts(self.orig_proc.body)
src/exo/effectcheck.py:1016: in map_stmts
    sub_body_eff = self.map_stmts(stmt.body)
src/exo/effectcheck.py:1044: in map_stmts
    self.check_bounds(stmt.name, shape, body_eff)
src/exo/effectcheck.py:791: in check_bounds
    self.check_in_bounds(sym, shape, e, y)
src/exo/effectcheck.py:775: in check_in_bounds
    e = self.expr_to_smt(e)
src/exo/effectcheck.py:612: in expr_to_smt
    return self.sym_to_smt(expr.name, expr.type)
src/exo/effectcheck.py:587: in sym_to_smt
    return self.env[sym]
/usr/lib/python3.9/collections/__init__.py:941: in __getitem__
    return self.__missing__(key)            # support subclasses that define __missing__
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = ChainMap({}, {i_3: i_3}, {n_1: n_1, arr_stride_0_7: arr_stride_0_7, tmp_stride_0_8: tmp_stride_0_8}, {})
key = i_5

    def __missing__(self, key):
>       raise KeyError(key)
E       KeyError: i_5

/usr/lib/python3.9/collections/__init__.py:933: KeyError
================================= short test summary info =================================
FAILED tests/test_schedules.py::test_new_expression_parsing - KeyError: i_5
==================================== 1 failed in 0.19s ====================================

During parsing, variable i_5 is captured as the variable i from the new expression. However, this is the variable i outside the loop definition.