fix: ensure screenshots are recognized artifacts

[alexplischke]

Description

A platform side change (/assets endpoint) moved screenshot files to the screenshots field. Prior to this change, saucectl was ignoring this field as it expected screenshots to appear on the root level (as do other files).

Before fix:

❯ saucectl artifacts list 5648b0fc31c644b78621cf006ad899b3
┌────────────────────────────────────────────────┐
│ Items                                          │
────────────────────────────────────────────────
│ index.html                                     │
│ 583f7f084ebd4ef4b73abc88b09a78e9.last-run.json │
│ log.json                                       │
│ console.log                                    │
│ config.yml                                     │
│ junit.xml                                      │
│ video.mp4                                      │
│ flags.json                                     │
│ sauce-test-report.json                         │
└────────────────────────────────────────────────┘

After fix:

❯ saucectl artifacts list 5648b0fc31c644b78621cf006ad899b3

┌─────────────────────────────────────────────────────────────────┐
│ Items                                                           │
─────────────────────────────────────────────────────────────────
│ 660938d924107f5889cdb401f0417855fbd326f0.png                    │
│ 6eea30518519a29b942c24b7eec882e2c31a029e.png                    │
│ fc53f633a77f60048da6cffd8cee2b424378cd49.png                    │
│ screen-capture-png-02c5050b38fd8609e580a1db8238ba7cc9c6f8c7.png │
│ screenshot-56cd48708adc9c65ea0a247630c94e6504490b0c.png         │
│ screenshot-96f80502c0a1278713b7ab28522f9d97b0c97a89.png         │
│ screenshot.png                                                  │
│ console.log                                                     │
│ sauce-test-report.json                                          │
│ junit.xml                                                       │
│ log.json                                                        │
│ index.html                                                      │
│ config.yml                                                      │
│ video.mp4                                                       │
│ 583f7f084ebd4ef4b73abc88b09a78e9.last-run.json                  │
│ flags.json                                                      │
└─────────────────────────────────────────────────────────────────┘