Update getAuthSchemes javadoc (#1930)

Updates javadoc for ServiceIndex::getAuthSchemes to say the returned
order is alphabetical. Tests were updated in #1915 to assert this
ordering for ServiceIndex::getEffectiveAuthSchemes, but it also
made the same update for the ServiceIndex::getAuthSchemes test.
The PR didn't include a javadoc update, so the purpose of this PR
is to fix that.

smithy-model/src/main/java/software/amazon/smithy/model/knowledge/ServiceIndex.java

@@ -127,6 +127,8 @@ private Model getModel() {
      * <p>An <em>auth defining trait</em> is a trait that is marked with
      * the {@code smithy.api#authDefinition} trait.
      *
+     * <p>The returned map is ordered alphabetically by absolute shape ID.
+     *
      * <p>An empty map is returned if {@code id} cannot be found in the
      * model or is not a service shape.
      *
@@ -149,7 +151,7 @@ public Map<ShapeId, Trait> getAuthSchemes(ToShapeId service) {
      *
      * <p>The returned map is provided in the same order as the values in the
      * {@code auth} trait if an auth trait is present, otherwise the result
-     * returned is ordered alphabetically by absolute shape id.
+     * returned is ordered alphabetically by absolute shape ID.
      *
      * <p>An empty map is returned if {@code service} cannot be found in the
      * model or is not a service shape.
@@ -213,7 +215,7 @@ public Map<ShapeId, Trait> getEffectiveAuthSchemes(ToShapeId service, AuthScheme
      *
      * <p>The returned map is provided in the same order as the values in the
      * {@code auth} trait if an auth trait is present, otherwise the result
-     * returned is ordered alphabetically by absolute shape id.
+     * returned is ordered alphabetically by absolute shape ID.
      *
      * <p>An empty map is returned if {@code service} shape cannot be found
      * in the model or is not a service shape. An empty map is returned if