Fix runtime interface client workflows to use local serialization dependency

Add local build step for aws-lambda-java-serialization before building runtime interface client.

## Why This Fix is Needed

The runtime interface client depends on aws-lambda-java-serialization version 1.1.6,
but this version doesn't exist in Maven Central yet. By building and installing the
serialization package locally first, we ensure:

1. The correct version (1.1.6) is available in the local Maven repository
2. The runtime interface client build won't fail looking for a non-existent version on Maven Central
3. The workflow tests the actual code changes together

## Changes Made

- runtime-interface-client_merge_to_main.yml: Added local serialization build step
- runtime-interface-client_pr.yml: Added local serialization build step to both smoke-test and build jobs

This ensures CI/CD pipeline works correctly with the new dependency versions.

Author: PartiallyUntyped

.github/workflows/runtime-interface-client_merge_to_main.yml

@@ -47,6 +47,10 @@ jobs:
     - name: Available buildx platforms
       run: echo ${{ steps.buildx.outputs.platforms }}
 
+    - name: Build and install serialization dependency locally
+      working-directory: ./aws-lambda-java-serialization
+      run: mvn clean install -DskipTests
+
     - name: Test Runtime Interface Client xplatform build - Run 'build' target
       working-directory: ./aws-lambda-java-runtime-interface-client
       run: make build

.github/workflows/runtime-interface-client_pr.yml

@@ -23,6 +23,10 @@ jobs:
         java-version: 8
         distribution: corretto
 
+    - name: Build and install serialization dependency locally
+      working-directory: ./aws-lambda-java-serialization
+      run: mvn clean install -DskipTests
+
     - name: Runtime Interface Client smoke tests - Run 'pr' target
       working-directory: ./aws-lambda-java-runtime-interface-client
       run: make pr
@@ -51,6 +55,10 @@ jobs:
     - name: Available buildx platforms
       run: echo ${{ steps.buildx.outputs.platforms }}
 
+    - name: Build and install serialization dependency locally
+      working-directory: ./aws-lambda-java-serialization
+      run: mvn clean install -DskipTests
+
     - name: Test Runtime Interface Client xplatform build - Run 'build' target
       working-directory: ./aws-lambda-java-runtime-interface-client
       run: make build