Don't create a release for every PR merged to master

[SeanKilleen]

I initially thought this would be nice, but now I'd really prefer for the release build to run on my command rather than as part of the main process. Too much noise otherwise, especially with dependabot.

Right now, the process is:

• Build/release on every push to master
• Create and push a tag
• Run the master branch build

What we'd want instead:

• Build on every push to master and make sure releasing is possible
• Upon creating a release, build + add artifacts to release + publish nuget.