README: fix coverage badge link to point at correct CI job

The badge linked to ?job=test-gpu, but the coverage-producing job in
.gitlab-ci.yml is named gpu, so the link 404'd.

Author: john00003

README.md

@@ -1,7 +1,7 @@
 # libplacebo
 
 [![gitlab-ci badge](https://code.videolan.org/videolan/libplacebo/badges/master/pipeline.svg)](https://code.videolan.org/videolan/libplacebo/pipelines)
-[![gitlab-ci coverage](https://code.videolan.org/videolan/libplacebo/badges/master/coverage.svg)](https://code.videolan.org/videolan/libplacebo/-/jobs/artifacts/master/file/coverage/index.html?job=test-gpu)
+[![gitlab-ci coverage](https://code.videolan.org/videolan/libplacebo/badges/master/coverage.svg)](https://code.videolan.org/videolan/libplacebo/-/jobs/artifacts/master/file/coverage/index.html?job=gpu)
 [![GitHub](https://img.shields.io/github/sponsors/haasn?logo=github)](https://github.com/sponsors/haasn)
 [![PayPal](https://img.shields.io/badge/donate-PayPal-blue.svg?logo=paypal)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=SFJUTMPSZEAHC)
 [![Patreon](https://img.shields.io/badge/pledge-Patreon-red.svg?logo=patreon)](https://www.patreon.com/haasn)