Prevent upload-artifact step from causing CI failure

This step has been failing way more than reasonable across my various repos.

    With the provided path, there will be 1 file uploaded
    Artifact name is valid!
    Root directory input is valid!
    Attempt 1 of 5 failed with error: Request timeout: /twirp/github.actions.results.api.v1.ArtifactService/CreateArtifact. Retrying request in 3000 ms...
    Attempt 2 of 5 failed with error: Request timeout: /twirp/github.actions.results.api.v1.ArtifactService/CreateArtifact. Retrying request in 6029 ms...
    Attempt 3 of 5 failed with error: Request timeout: /twirp/github.actions.results.api.v1.ArtifactService/CreateArtifact. Retrying request in 8270 ms...
    Attempt 4 of 5 failed with error: Request timeout: /twirp/github.actions.results.api.v1.ArtifactService/CreateArtifact. Retrying request in 12577 ms...
    Error: Failed to CreateArtifact: Failed to make request after 5 attempts: Request timeout: /twirp/github.actions.results.api.v1.ArtifactService/CreateArtifact

Author: dtolnay

.github/workflows/ci.yml

@@ -31,6 +31,7 @@ jobs:
         with:
           name: Cargo.lock
           path: _skeptic/Cargo.lock
+        continue-on-error: true
 
   outdated:
     name: Outdated