tests: avoid test crash getting @elastic/elasticsearch version

[trentm]

The tests were using require('@elastic/elasticsearch/package.json')
which runs afoul of EOL'd folder mappings in "exports"
(https://nodejs.org/api/all.html#DEP0148) with current ES client
versions and the latest node v17 nightly.

Fixes: #2350

Checklist

• Implement code
• Commit message follows commit guidelines

[apmmachine]

💚 Build Succeeded

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Build stats

• Start Time: 2021-09-27T19:39:36.570+0000

• Duration: 22 min 39 sec

• Commit: 8e61dbd

Test stats 🧪

Test	Results
Failed	0
Passed	6
Skipped	4
Total	10

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• run module tests for <modules> : Run TAV tests for one or more modules, where <modules> can be either a comma separated list of modules (e.g. memcached,redis) or the string literal ALL to test all modules

• run benchmark tests : Run the benchmark test only.

[trentm]

I manually did an edge run to test again with the latest Node.js nightly and that passed: https://apm-ci.elastic.co/blue/organizations/jenkins/apm-agent-nodejs%2Fapm-agent-nodejs-mbp/detail/PR-2351/2/pipeline/189

[astorm]

👍 does what it says it does, and keeps up up to date with the node.js release train. Approving.

[astorm]

👍 for this being in devDependencies