Remove ubuntu-16.04 and add missing links for nix/go

[catthehacker]

Fixes #645

GitHub removes ubuntu-16.04 environment since it reached standard EOL.

We will follow that change and remove default images for ubuntu-16.04 but it doesn't prevent users from using that platform.

To still use ubuntu-16.04, apart from being defined in workflow, it has to be specified via -P/--platform flags, e.g.:

act -P ubuntu-16.04=ghcr.io/catthehacker/ubuntu:act-16.04

.actrc:

-P ubuntu-16.04=node:12-stretch-slim

I'm not planning on removing Ubuntu 16.04 images, but they will eventually stop receiving updates so I advise on migrating to newer Ubuntu.

---

fix: remove specific platform versions: remove mention of specific versions to remove confusion since platforms such as macos-11 or windows-2022, windows-2016 exist

Platforms still will be properly inferred from workflow and README.md mentions about macOS and Windows

  ~/go/src/github.com/nektos/act cat/fix/remove-ubuntu-16.04 *14 ❯ go run main.go -W .github/workflows/test-windows.yml                                12:20:27 PM
[test-windows.yml/test] 🚧  Skipping unsupported platform -- Try running with `-P windows-latest=...`
  ~/go/src/github.com/nektos/act cat/fix/remove-ubuntu-16.04 *14 ❯ go run main.go -W .github/workflows/test-windows.yml                                12:21:46 PM
[test-windows.yml/test] 🚧  Skipping unsupported platform -- Try running with `-P windows-2016=...`
  ~/go/src/github.com/nektos/act cat/fix/remove-ubuntu-16.04 *14 ❯

[codecov]

Codecov Report

Merging #821 (a65fe92) into master (0f04942) will increase coverage by 4.67%.
The diff coverage is 62.43%.

@@            Coverage Diff             @@
##           master     #821      +/-   ##
==========================================
+ Coverage   49.27%   53.94%   +4.67%     
==========================================
  Files          23       23              
  Lines        2401     2697     +296     
==========================================
+ Hits         1183     1455     +272     
- Misses       1090     1093       +3     
- Partials      128      149      +21     

Impacted Files	Coverage Δ
pkg/container/docker_build.go	0.00% <0.00%> (ø)
pkg/container/docker_run.go	1.76% <0.00%> (-0.17%)	⬇️
pkg/common/git.go	52.55% <30.88%> (-7.24%)	⬇️
pkg/runner/runner.go	68.96% <33.33%> (-7.51%)	⬇️
pkg/model/planner.go	52.14% <43.33%> (+19.06%)	⬆️
pkg/model/workflow.go	51.08% <62.68%> (+25.37%)	⬆️
pkg/container/docker_pull.go	36.17% <64.70%> (+17.98%)	⬆️
pkg/runner/expression.go	85.38% <71.87%> (-1.26%)	⬇️
pkg/runner/step_context.go	78.92% <79.90%> (+9.97%)	⬆️
pkg/runner/run_context.go	79.70% <91.95%> (+3.29%)	⬆️
... and 7 more

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