Replace Travis-CI with GitHub "CI" Action

[JasonPierce]

With the advancement of GitHub Actions there is no longer a need/value in using an external service for Continuous Integration. Replace the existing Travis-CI setup with a new GitHub Action

The following back-of-napkin script is untested, but it should look something like:

name: CI

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
      # Step 1: Checkout the repository
      - name: Checkout code
        uses: actions/checkout@v4

      # Step 2: Set up .NET Core SDK
      - name: Setup .NET Core SDK
        uses: actions/setup-dotnet@v4
        with:
          dotnet-version: '1.0.x'

      # Step 3: Install dependencies
      - name: Install dependencies
        run: |
          sudo apt-get update
          sudo apt-get install -y gettext libcurl4-openssl-dev libicu-dev libssl-dev libunwind8 zlib1g

      # Step 4: Install the specific .NET Core SDK version
      - name: Install .NET Core CLI
        run: |
          export DOTNET_INSTALL_DIR="$PWD/.dotnetcli"
          curl -sSL https://raw.githubusercontent.com/dotnet/cli/rel/1.0.0/scripts/obtain/dotnet-install.sh | bash /dev/stdin --version latest --install-dir "$DOTNET_INSTALL_DIR"
          echo "$DOTNET_INSTALL_DIR" >> $GITHUB_PATH

      # Step 5: Restore the dependencies
      - name: Restore dependencies
        run: dotnet restore

      # Step 6: Run tests
      - name: Run tests
        run: dotnet test ./Rijndael256.Tests/Rijndael256.Tests.csproj -c Release -f netcoreapp1.0