docs: update title of v9 injectable migration guide (#34125)

The missing-injectable migration has been updated to handle a breaking change that is
unrelated to missing ´@Injectable` decorators. Though, the breaking change will be handled
as part of this migration since we did not want to create another migration (with all the boilerplate etc.)

The guide has been already updated to reflect the new pattern the migration handles, but we
should also rename the title of the guide to something that also mentions the other pattern.

Not renaming the guide URL since it is referenced in past releases and it's safer to keep the old
URL. The important thing is to change the actual rendered title.

PR Close #34125

aio/content/guide/migration-injectable.md

@@ -1,4 +1,4 @@
-# Migration to Add Missing `@Injectable()` Decorators
+# Migration for missing `@Injectable()` decorators and incomplete provider definitions
 
 ### What does this schematic do?
 

aio/content/guide/updating-to-version-9.md

@@ -102,7 +102,7 @@ Read about the migrations the CLI handles for you automatically:
 
 - [Migrating from `Renderer` to `Renderer2`](guide/migration-renderer)
 - [Migrating undecorated classes](guide/migration-undecorated-classes)
-- [Migrating missing `@Injectable()` decorators](guide/migration-injectable)
+- [Migrating missing `@Injectable()` decorators and incomplete provider definitions](guide/migration-injectable)
 - [Migrating dynamic queries](guide/migration-dynamic-flag)
 - [Migrating to the new `$localize` i18n support](guide/migration-localize)
 - [Migrating `ModuleWithProviders`](guide/migration-module-with-providers)