Fix new flake8 E741 error from using `l` variable

The just-updated flake8 package hits a bunch of:

    E741 ambiguous variable name 'l'

warnings.  This commit renames them all from `l` to `lst` (they are all
list values) to avoid the error.

tests/test_opaque_types.py

@@ -4,21 +4,21 @@ from pybind11_tests import ConstructorStats, UserType
 
 
 def test_string_list():
-    l = m.StringList()
-    l.push_back("Element 1")
-    l.push_back("Element 2")
-    assert m.print_opaque_list(l) == "Opaque list: [Element 1, Element 2]"
-    assert l.back() == "Element 2"
+    lst = m.StringList()
+    lst.push_back("Element 1")
+    lst.push_back("Element 2")
+    assert m.print_opaque_list(lst) == "Opaque list: [Element 1, Element 2]"
+    assert lst.back() == "Element 2"
 
-    for i, k in enumerate(l, start=1):
+    for i, k in enumerate(lst, start=1):
         assert k == "Element {}".format(i)
-    l.pop_back()
-    assert m.print_opaque_list(l) == "Opaque list: [Element 1]"
+    lst.pop_back()
+    assert m.print_opaque_list(lst) == "Opaque list: [Element 1]"
 
     cvp = m.ClassWithSTLVecProperty()
     assert m.print_opaque_list(cvp.stringList) == "Opaque list: []"
 
-    cvp.stringList = l
+    cvp.stringList = lst
     cvp.stringList.push_back("Element 3")
     assert m.print_opaque_list(cvp.stringList) == "Opaque list: [Element 1, Element 3]"
 

tests/test_pytypes.py

@@ -7,11 +7,11 @@ from pybind11_tests import debug_enabled
 
 def test_list(capture, doc):
     with capture:
-        l = m.get_list()
-        assert l == ["overwritten"]
+        lst = m.get_list()
+        assert lst == ["overwritten"]
 
-        l.append("value2")
-        m.print_list(l)
+        lst.append("value2")
+        m.print_list(lst)
     assert capture.unordered == """
         Entry at position 0: value
         list item 0: overwritten

tests/test_sequences_and_iterators.py

@@ -131,9 +131,9 @@ def test_python_iterator_in_cpp():
         m.iterator_to_list(iter(bad_next_call, None))
     assert str(excinfo.value) == "py::iterator::advance() should propagate errors"
 
-    l = [1, None, 0, None]
-    assert m.count_none(l) == 2
-    assert m.find_none(l) is True
+    lst = [1, None, 0, None]
+    assert m.count_none(lst) == 2
+    assert m.find_none(lst) is True
     assert m.count_nonzeros({"a": 0, "b": 1, "c": 2}) == 2
 
     r = range(5)

tests/test_stl.py

@@ -6,11 +6,11 @@ from pybind11_tests import UserType
 
 def test_vector(doc):
     """std::vector <-> list"""
-    l = m.cast_vector()
-    assert l == [1]
-    l.append(2)
-    assert m.load_vector(l)
-    assert m.load_vector(tuple(l))
+    lst = m.cast_vector()
+    assert lst == [1]
+    lst.append(2)
+    assert m.load_vector(lst)
+    assert m.load_vector(tuple(lst))
 
     assert m.cast_bool_vector() == [True, False]
     assert m.load_bool_vector([True, False])
@@ -24,9 +24,9 @@ def test_vector(doc):
 
 def test_array(doc):
     """std::array <-> list"""
-    l = m.cast_array()
-    assert l == [1, 2]
-    assert m.load_array(l)
+    lst = m.cast_array()
+    assert lst == [1, 2]
+    assert m.load_array(lst)
 
     assert doc(m.cast_array) == "cast_array() -> List[int[2]]"
     assert doc(m.load_array) == "load_array(arg0: List[int[2]]) -> bool"
@@ -34,9 +34,9 @@ def test_array(doc):
 
 def test_valarray(doc):
     """std::valarray <-> list"""
-    l = m.cast_valarray()
-    assert l == [1, 4, 9]
-    assert m.load_valarray(l)
+    lst = m.cast_valarray()
+    assert lst == [1, 4, 9]
+    assert m.load_valarray(lst)
 
     assert doc(m.cast_valarray) == "cast_valarray() -> List[int]"
     assert doc(m.load_valarray) == "load_valarray(arg0: List[int]) -> bool"