test(cmd-api-server): fix flaky runtime-plugin-imports test

[petermetz]

This is a flaky test case meaning that it cannot be reliably reproduced, it only happens
every now and then which of course makes it harder to fix as well.

There is a clue I found based on the error message printed by Jest though:
https://stackoverflow.com/a/50793993

Logs

logs_12177.zip

ReferenceError: You are trying to `import` a file after the Jest environment has been torn down. From packages/cactus-test-cmd-api-server/src/test/typescript/integration/runtime-plugin-imports.test.ts.

      346 |
      347 |       // eslint-disable-next-line @typescript-eslint/no-var-requires
    > 348 |       const pluginPackage = require(/* webpackIgnore: true */ packagePath);
          |                             ^
      349 |       const createPluginFactory = pluginPackage.createPluginFactory as PluginFactoryFactory;
      350 |       const pluginFactoryOptions: IPluginFactoryOptions = {
      351 |         pluginImportType: pluginImport.type,

      at ApiServer.instantiatePlugin (packages/cactus-cmd-api-server/src/main/typescript/api-server.ts:348:29)
          at runMicrotasks (<anonymous>)
      at ApiServer.initPluginRegistry (packages/cactus-cmd-api-server/src/main/typescript/api-server.ts:313:22)
      at ApiServer.getOrInitPluginRegistry (packages/cactus-cmd-api-server/src/main/typescript/api-server.ts:289:33)