Bump Liquid to 5.11.0 (#2012)

This commit reverts the Inline Snippets tag (#2001) and bumps
Liquid to 5.11. For now, the inclusion of Inline Snippets
in the latest Liquid release is being treated as a bug.

While #2001 does implement the scope contained in RFC#1916,
we need to take a step back to make sure we’re setting our
sights high enough with this feature, and that we’re truly
supporting theme developers in the ways they need.

If you have any feedback, please leave a comment on RFC#1916.

- Liquid Developer Tools

test/unit/variable_unit_test.rb

@@ -161,8 +161,8 @@ class VariableUnitTest < Minitest::Test
     end
   end
 
-  def test_rigid_filter_argument_parsing
-    with_error_modes(:rigid) do
+  def test_strict2_filter_argument_parsing
+    with_error_modes(:strict2) do
       # optional colon
       var = create_variable(%(n | f1 | f2:))
       assert_equal([['f1', []], ['f2', []]], var.filters)