Fix main workflow to use proper alr for base branch (#235)

* Use proper alr for the base branch

* Fix: set up compiler before devel alr

.github/workflows/main.yml

@@ -10,7 +10,19 @@ jobs:
       with:
         repo-token: "${{ secrets.GITHUB_TOKEN }}"
 
-    - uses: alire-project/setup-alire@latest-stable
+    - name: Set up stable `alr`
+      if: contains(github.base_ref, 'stable-')
+      uses: alire-project/setup-alire@latest-stable
+
+    - name: Set up GNAT for devel `alr`
+      if: contains(github.base_ref, 'devel-')
+      uses: ada-actions/toolchain@ce2020
+      with:
+        distrib: fsf
+
+    - name: Set up devel `alr`
+      if: contains(github.base_ref, 'devel-')
+      uses: alire-project/setup-alire@latest-devel
 
     - run: alr index --list