gst-build: Disabling uploading of artifacts for now

gst-build: Disabling uploading of artifacts for now

It seems to be timing out with high frequency only on Windows runners.

```
Version:      12.8.0
00:47
Git revision: 1b659122
Git branch:   12-8-stable
GO version:   go1.13.7
Built:        2020-02-22T03:03:07+0000
OS/Arch:      windows/amd64
Uploading artifacts...
gst-build/build/meson-logs/: found 2 matching files
WARNING: Failed to load system CertPool: crypto/x509: system root pool is not available on Windows
ERROR: Job failed (system failure): aborted: <nil>
```

See: https://gitlab.freedesktop.org/gstreamer/gst-ci/-/merge_requests/261