Fix test target

[twpayne]

This PR:

• Removes stray code added in feat: support custom GITHUB_RUN_ID, GITHUB_RUN_NUMBER #369 (presumably added accidentally: examples/workflows does not exist).
• Adds go test ./... to the test target.

Note that the test fail on my Ubuntu machine:

[push/lint    ] 🚀  Start image=node:12.6-buster-slim
[push/test    ] 🚀  Start image=node:12.6-buster-slim
[push/test    ]   🐳  docker run image=node:12.6-buster-slim entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[push/lint    ]   🐳  docker run image=node:12.6-buster-slim entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[push/test    ]   🐳  docker cp src=/home/twp/src/github.com/nektos/act/. dst=/github/workspace
[push/lint    ]   🐳  docker cp src=/home/twp/src/github.com/nektos/act/. dst=/github/workspace
[push/test    ] ⭐  Run actions/checkout@v2
[push/test    ]   ✅  Success - actions/checkout@v2
[push/test    ] ⭐  Run actions/setup-go@v1
[push/test    ]   ☁  git clone 'https://github.com/actions/setup-go' # ref=v1
[push/test    ] Unable to resolve v1: reference not found
[push/test    ]   ❌  Failure - actions/setup-go@v1
Error: reference not found
exit status 1

I think this is due to issue #311.

[cplee]

thanks @twpayne !