build: fix lint failures (#21692)

Fixes a few lint failures that got through, because the related PRs were opened before the
check was introduced.

(cherry picked from commit 0091015)

Author: crisbeto

scripts/check-mdc-exports-config.ts

@@ -18,6 +18,10 @@ export const config = {
       '_MatAutocompleteTriggerBase',
       '_MatAutocompleteOriginBase'
     ],
+    'mdc-autocomplete/testing': [
+      // Private base classes that are only exported for MDC.
+      '_MatAutocompleteHarnessBase'
+    ],
     'mdc-core': [
       // Private base classes that are only exported for MDC.
       '_MatOptionBase',
@@ -33,6 +37,11 @@ export const config = {
       // Private base class that is only exported for MDC.
       '_MatMenuBase'
     ],
+    'mdc-menu/testing': [
+      // Private base class that is only exported for MDC.
+      '_MatMenuHarnessBase',
+      '_MatMenuItemHarnessBase'
+    ],
     'mdc-paginator': [
       // Private base class that is only exported for MDC.
       '_MatPaginatorBase'
@@ -51,6 +60,10 @@ export const config = {
       // Private base class that is only exported for MDC.
       '_MatSelectBase'
     ],
+    'mdc-select/testing': [
+      // Private base class that is only exported for MDC.
+      '_MatSelectHarnessBase'
+    ],
     'mdc-slide-toggle': [
       // Private module used to provide some common functionality.
       '_MatSlideToggleRequiredValidatorModule'