ogma-cli: Introduce CI test job. Refs #139.

Ogma doesn't currently rely on Travis CI for testing, because Travis is
setup to run on all NASA repositories and we run out of cycles very
quickly. We need to automate the testing process as much as possible
regardless, and follow our own guide for compliance with NPR7150.2D but
using Github instead of Travis CI.

This commit introduces a Github Actions file that builds the source code
in every push action and with every pull requests.

.github/workflows/repo-ghc-8.6-cabal-2.4.yml

@@ -0,0 +1,63 @@
+name: install-hackage-ghc-8.6-cabal-2.4
+
+# Trigger the workflow on push or pull request
+on:
+  - pull_request
+  - push
+
+jobs:
+  cabal:
+    name: ${{ matrix.os }} / ghc ${{ matrix.ghc }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+        cabal: ["2.4"]
+        ghc:
+          - "8.6"
+
+    steps:
+
+    - uses: haskell-actions/setup@main
+      id: setup-haskell-cabal
+      name: Setup Haskell
+      with:
+        ghc-version: ${{ matrix.ghc }}
+        cabal-version: ${{ matrix.cabal }}
+
+    - name: Prepare environment
+      run: |
+        echo "$HOME/.ghcup/bin" >> $GITHUB_PATH
+        echo "$HOME/.cabal/bin" >> $GITHUB_PATH
+
+    - uses: actions/checkout@v4
+
+    - name: Create sandbox
+      run: |
+        echo "$PWD/.cabal-sandbox/bin" >> $GITHUB_PATH
+        cabal v1-sandbox init
+
+    - name: Install dependencies
+      run: |
+        cabal v1-install alex happy
+
+    - name: Install ogma
+      run: |
+        # Some tests need the ogma executable to be in the path, which won't
+        # happen until installation completes successfully (which only happens
+        # after tests if running tests is enabled). We therefore need to run
+        # the installation twice: once without --run-tests, and again with
+        # --run-tests.
+        #
+        # We still --enable-tests in the first compilation to make sure that
+        # the dependencies do not change and cabal does not change the
+        # installation plan (which would mean we'd be running the tests with a
+        # version of ogma compiled with different dependencies).
+        cabal v1-install ogma-**/ --enable-tests
+
+    - name: Test all packages
+      run: |
+        # We want to document the build process, and get detailed information
+        # if there is a problem (or if all goes well). We therefore execute the
+        # installation with -j1.
+        cabal v1-install ogma-**/ --enable-tests --run-tests -j1