[CI] occasional npm "Unexpected end of JSON input while parsing near ..." error

We have [started seeing an issue in the master branch](https://apm-ci.elastic.co/blue/organizations/jenkins/apm-agent-nodejs%2Fapm-agent-nodejs-mbp/detail/master/1028/pipeline) wherein `npm` seems to fail:

```
...
[2021-08-19T06:25:59.470Z] node_tests_1 | npm WARN deprecated b64@4.1.2: This module has moved and is now available at @hapi/b64. Please update your dependencies as this version is no longer maintained an may contain bugs and security issues.
[2021-08-19T06:26:02.777Z] node_tests_1 | npm WARN deprecated vise@3.0.2: This module has moved and is now available at @hapi/vise. Please update your dependencies as this version is no longer maintained an may contain bugs and security issues.
[2021-08-19T06:26:03.724Z] node_tests_1 | npm WARN deprecated urix@0.1.0: Please see https://github.com/lydell/urix#deprecated
[2021-08-19T06:26:04.297Z] node_tests_1 | npm WARN deprecated resolve-url@0.2.1: https://github.com/lydell/resolve-url#deprecated
[2021-08-19T06:26:05.688Z] node_tests_1 | npm ERR! Unexpected end of JSON input while parsing near '...dependencies":{"sax":'
[2021-08-19T06:26:05.688Z] node_tests_1 |
[2021-08-19T06:26:05.688Z] node_tests_1 | npm ERR! A complete log of this run can be found in:
[2021-08-19T06:26:05.688Z] node_tests_1 | npm ERR! /tmp/.npm/_logs/2021-08-19T06_26_05_472Z-debug.log
[2021-08-19T06:26:06.260Z] docker_node_tests_1 exited with code 1
[2021-08-19T06:26:06.260Z] Aborting on container exit...
script returned exit code 1
```