Rewrite brittle test to more resilient, ignoring FORCE_COLOR (#187539)

## Summary
We've seen the tests go both ways on the new infra. Sometimes the
received object would have, sometimes it wouldn't have `FORCE_COLOR`.
The value comes from here:
41eb6e2b12/packages/kbn-cli-dev-mode/src/using_server_process.ts (L39)
- meaning `process.stdout.isTTY` is not always true?

Here, it fails because the snapshot doesn't have the flag:
https://buildkite.com/elastic/kibana-on-merge/builds/47027#01907bbb-3fae-48c4-95ca-85118ba2c2b8
Here, it because the snapshot has the flag:
https://buildkite.com/elastic/kibana-pull-request/builds/219429

This PR tries to ignore that part of the received object.

packages/kbn-cli-dev-mode/src/dev_server.test.ts

@@ -122,31 +122,17 @@ describe('#run$', () => {
   it('starts the dev server with the right options', () => {
     run(new DevServer(defaultOptions)).unsubscribe();
 
-    expect(execa.node.mock.calls).toMatchInlineSnapshot(`
+    expect(execa.node.mock.calls).toBeDefined();
-      Array [
+
-        Array [
+    const [scriptName, scriptArgs, execaOptions] = execa.node.mock.calls[0];
-          "some/script",
+
-          Array [
+    expect(scriptName).toBe('some/script');
-            "foo",
+    expect(scriptArgs).toEqual(['foo', 'bar', '--logging.json=false']);
-            "bar",
+    expect(execaOptions).toMatchObject({
-            "--logging.json=false",
+      env: expect.objectContaining({ ELASTIC_APM_SERVICE_NAME: 'kibana', isDevCliChild: 'true' }),
-          ],
+      nodeOptions: ['--inheritted', '--exec', '--argv'],
-          Object {
+      stdio: 'pipe',
-            "env": Object {
+    });
-              "<inheritted process.env>": true,
-              "ELASTIC_APM_SERVICE_NAME": "kibana",
-              "isDevCliChild": "true",
-            },
-            "nodeOptions": Array [
-              "--inheritted",
-              "--exec",
-              "--argv",
-            ],
-            "stdio": "pipe",
-          },
-        ],
-      ]
-    `);
   });
 
   it('writes stdout and stderr lines to logger', () => {