Merge torrust#924: ci: nightly build for coverage

3d567c8 ci: nightly build for coverage (Cameron Garnham)

Pull request description:

ACKs for top commit:
  da2ce7:
    ACK 3d567c8

Tree-SHA512: 19843c2812ae606f25b076a6ba5fe53df1025e913f11d238a75b3526e4288edcac20a6921e25cb29817b71547851baeab9b9de95206aeee81159b07b2aba9f2d

Author: da2ce7

.github/workflows/coverage.yaml

@@ -36,7 +36,7 @@ jobs:
 
       - id: setup
         name: Setup Toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
           toolchain: nightly
           components: llvm-tools-preview