chore: include @aws-cdk/service-spec-importers in service spec update (#27854)

Fixes `@aws-cdk/service-spec-importers` being outdated

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: mrgrain

.github/workflows/spec-update.yml

@@ -30,11 +30,11 @@ jobs:
       - name: Install ncu tool
         run: npm -g install lerna npm-check-updates
       - name: Run "ncu" for service spec packages
-        run: lerna exec --parallel ncu -- --upgrade --filter='@aws-cdk/aws-service-spec,@aws-cdk/service-spec-types' --target=latest
+        run: lerna exec --parallel ncu -- --upgrade --filter='@aws-cdk/aws-service-spec,@aws-cdk/service-spec-importers,@aws-cdk/service-spec-types' --target=latest
 
       # This will ensure the current lockfile is up-to-date with the dependency specifications
       - name: Install latest version & update lockfile
-        run: yarn upgrade @aws-cdk/aws-service-spec @aws-cdk/service-spec-types
+        run: yarn upgrade @aws-cdk/aws-service-spec @aws-cdk/service-spec-importers @aws-cdk/service-spec-types
 
       # Build @aws-cdk/spec2cdk and run L1 gen script to generate base files for new modules
       - name: Build @aws-cdk/spec2cdk