Current Heartbeat/Synthetics Docker image (snapshot) not working

[paulb-elastic]

Getting the following error with the beta.3 version of Synthetics in the heartbeat:8.0.0-SNAPSHOT Heartbeat image:

2021-06-17T19:53:25.437Z    INFO    synthexec/synthexec.go:224    stderr: Failed to run the test Error: EACCES: permission denied, mkdir '/usr/share/heartbeat/.synthetics/35/screenshots'
2021-06-17T19:53:25.437Z    INFO    synthexec/synthexec.go:224    stderr:     at Object.mkdirSync (fs.js:921:3)
2021-06-17T19:53:25.437Z    INFO    synthexec/synthexec.go:224    stderr:     at Runner.init (/usr/share/heartbeat/.node/node/lib/node_modules/@elastic/synthetics/src/core/runner.ts:357:5)
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:     at Runner.run (/usr/share/heartbeat/.node/node/lib/node_modules/@elastic/synthetics/src/core/runner.ts:367:10)
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:     at Object.run (/usr/share/heartbeat/.node/node/lib/node_modules/@elastic/synthetics/src/index.ts:45:25)
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:     at /usr/share/heartbeat/.node/node/lib/node_modules/@elastic/synthetics/src/cli.ts:175:25
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:     at processTicksAndRejections (internal/process/task_queues.js:97:5) {
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:   errno: -13,
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:   syscall: 'mkdir',
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:   code: 'EACCES',
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr:   path: '/usr/share/heartbeat/.synthetics/35/screenshots'
2021-06-17T19:53:25.438Z    INFO    synthexec/synthexec.go:224    stderr: }
2021-06-17T19:53:25.444Z    INFO    synthexec/synthexec.go:176    Command has completed(1): /usr/share/heartbeat/.node/node/bin/elastic-synthetics --inline --rich-events --outfd 3
2021-06-17T19:53:25.444Z    WARN    synthexec/synthexec.go:183    Error executing command '/usr/share/heartbeat/.node/node/bin/elastic-synthetics --inline --rich-events --outfd 3': exit status 1

Discussion with @andrewvc and this should be writing to /tmp in the image.