ci: Disable rustup self-updates (#68)

.github/workflows/sparse-registry.yml

@@ -19,7 +19,10 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
+      # When rustup is updated, it tries to replace its binary, which on Windows is somehow locked.
+      # This can result in the CI failure, see: https://github.com/rust-lang/rustup/issues/3029
       - run: |
+          rustup set auto-self-update disable
           rustup toolchain install nightly --profile minimal
           rustup default nightly