Add GitHub action for CI tests

[ssiccha]

This PR configures GitHub Actions to run the package tests. It was created by a script. You can view the results of the added GitHub action under: ${inspect_action_results_url}

This PR contains four commits which do:

• adds a file .github/workflows/CI.yml which configures GitHub Actions to run the package tests,
• removes the .travis.yml file if it exists in the package,
• adds a CI action badge to the README.md, if it found none, and
• removes the travis CI badge from the README.md, if it finds one.

Since this PR is generated automatically, please double-check that the last three commits do not break anything.

The added GitHub action contains a job test, which runs your package's tests using the same scripts from https://github.com/gap-system/pkg-ci-scripts as previously did Travis. By default it tests your package with the following gap branches:

• master
• stable-4.11
• stable-4.10 The action also contains a job manual, which compiles your package's documentation with latex and uploads the resulting pdf as an artifact, which means that it can be downloaded once all jobs of the action completed.

If you want to adjust which tests are run have a look at the documentation of the job matrix.

If you need to compile packages to load your package, set the input GAP_PKGS_TO_BUILD for the action gap-actions/setup-gap-for-packages@v1 to a space-separated list of packages as follows:

- uses: gap-actions/setup-gap-for-packages@v1
  with:
    GAPBRANCH: ${{ matrix.gap-branch }}
    GAP_PKGS_TO_BUILD: "<list-of-packages>"

If you need to clone the development version of packages set the input GAP_PKGS_TO_CLONE for the action gap-actions/setup-gap-for-packages@v1 to a space-separated list of packages as follows:

- uses: gap-actions/setup-gap-for-packages@v1
  with:
    GAPBRANCH: ${{ matrix.gap-branch }}
    GAP_PKGS_TO_CLONE: "<list-of-packages>"

Notice that you may also have to set inputs for the action gap-actions/setup-gap-for-packages@v1 in the job manual.

The custom gap actions which are used by the added action can be found at: https://github.com/gap-actions