CI: Consider automatically uploading build artifacts during PR workflows

[erichte-ibm]

When test cases fail in the CI environment, it might be useful to be able to download and run in a debugger -- this is particularly useful if the errors seem to only occur in CI.

Furthermore, this may be useful for supplying prebuilt binaries for testing purposes, if for example you want to propose a fix via PR, and can then point the reporter of the issue to the compiled artifact.

NOTE: This should probably not be an automatic workflow. It's probably a good idea to require manual intervention so that the code can at least be briefly inspected for malicious intent before distributing a binary.