test: call the ladder positions rungs, as ADR 0011 does

The glossary now defines the precedence ladder and its rungs (PR DOI-USGS#405),
which makes the one identifier still saying "tiers" for ladder positions
a core-term misspelling rather than a stray. The file's own comments
already say rung. ADR 0011's compliance citation is annotated the way
ADR 0008 annotated the wateruse rename, so the reference stays true.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JAEQqs7XzQHGQQi2KakuXD

Author: thodson-usgs

docs/source/architecture/decisions/0011-configuration-profiles.rst

@@ -210,7 +210,8 @@ Satisfied. In ``tests/configuration_test.py``:
 
 - ``test_several_named_profiles_are_selected_independently`` -- one block,
   a different profile per adapter.
-- ``test_a_named_profile_layers_per_key_over_the_tiers_below`` -- a profile
+- ``test_a_named_profile_layers_per_key_over_the_rungs_below`` (named
+  ``..._the_tiers_below`` when this decision was taken) -- a profile
   inherits its adapter's default profile and the package-wide keys per key.
 - ``test_adding_a_named_profile_changes_nothing_until_it_is_selected`` -- a
   named profile is inert until something selects it.

tests/configuration_test.py

@@ -358,7 +358,7 @@ def test_several_named_profiles_are_selected_independently(config_file):
         assert configuration.concurrency(adapter="ngwmn") == 4
 
 
-def test_a_named_profile_layers_per_key_over_the_tiers_below(config_file):
+def test_a_named_profile_layers_per_key_over_the_rungs_below(config_file):
     """Selecting a profile replaces keys, never whole sources.
 
     Every level of the file overrides the one below it *per key* (ADR 0011), so