fix: build of Lambda layer broke in CI

[trentm]

The BRANCH_NAME=... make -C .ci dist failed on
cp: ../build/aws/elastic-apm-node-lambda-layer-...zip: No such file or directory
because the "../build/aws" dir had not been created.
This was broken in #2627.

This fixes the failure in the release pipeline for the v3.34.0 release: https://apm-ci.elastic.co/blue/organizations/jenkins/apm-agent-nodejs%2Fapm-agent-nodejs-mbp/detail/v3.34.0/1/pipeline

[2022-05-25T17:36:24.008Z] The lambda layer can be published as follows for dev work:
[2022-05-25T17:36:24.008Z]     aws lambda --output json publish-layer-version --layer-name '-dev-elastic-apm-node' --description ' dev Elastic APM Node.js agent lambda layer' --zip-file 'fileb://build/lambda-layer-zip/elastic-apm-node-lambda-layer.zip'
[2022-05-25T17:36:24.008Z] cp ../build/lambda-layer-zip/elastic-apm-node-lambda-layer.zip ../build/aws/elastic-apm-node-lambda-layer-v3.34.0.zip
[2022-05-25T17:36:24.008Z] cp: cannot create regular file '../build/aws/elastic-apm-node-lambda-layer-v3.34.0.zip': No such file or directory
[2022-05-25T17:36:24.008Z] Makefile:10: recipe for target 'dist' failed

[ghost]

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• Start Time: 2022-05-25T17:53:14.234+0000

• Duration: 20 min 22 sec

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Test	Results
Failed	0
Passed	254251
Skipped	0
Total	254251

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