Remove dependency on GNAT CE when building branch

.github/workflows/selftest.yml

@@ -9,6 +9,7 @@ on: pull_request
 jobs:
   setup-alire:
     strategy:
+      fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
         target: [stable, nightly, source]

action.yml

@@ -77,13 +77,44 @@ runs:
       id: find-gnat
       run: gnat --version && echo "available=true" >> $GITHUB_OUTPUT || echo "available=false" >> $GITHUB_OUTPUT
 
-    # Setup a GNAT if necessary to build from branch.
-    # We cannot use alr-install or setup-alire, as that creates infinite recursion.
-    - name: Install GNAT
+    # Setup a GNAT if necessary to build from branch. We cannot use alr-install
+    # or setup-alire, as that creates infinite recursion. Rather than relying
+    # on the old action that sets up CE editions, we rely on ourselves to
+    # install a stable alr and use it to install the toolchain we need.
+
+    # BEGIN TOOLCHAIN INSTALLATION
+
+    - name: Identify need for GNAT
       if: inputs.branch != '' && steps.find-gnat.outputs.available != 'true' && steps.cache-alr.outputs.cache-hit != 'true'
-      uses: ada-actions/toolchain@ce2020
-      with:
-        distrib: community
+      id: need-GNAT
+      shell: bash
+      run: echo "need=true" >> $GITHUB_OUTPUT
+
+    - name: Install GNAT (I)
+      if: steps.need-GNAT.outputs.need == 'true'
+      uses: alire-project/setup-alire@v3
+
+    - name: Install GNAT (II)
+      if: steps.need-GNAT.outputs.need == 'true'
+      shell: bash
+      run: |
+        alr install gnat_native gprbuild --prefix=$PWD/setup_alire_prefix
+        rm -rf ./alire_install && echo REMOVED stable alr used for toolchain install
+
+    - name: Install GNAT (III) - Add to path (Windows)
+      if: steps.need-GNAT.outputs.need == 'true' && runner.os == 'Windows'
+      shell: pwsh
+      run: |
+        $Target = Resolve-Path $PWD.Path\setup_alire_prefix\bin
+        Add-Content $env:GITHUB_PATH $Target
+
+    - name: Install GNAT (III) - Add to path (!Windows)
+      if: steps.need-GNAT.outputs.need == 'true' && runner.os != 'Windows'
+      shell: bash
+      run: |
+        readlink -f "$PWD/setup_alire_prefix/bin" >> $GITHUB_PATH
+
+    # END TOOLCHAIN INSTALLATION
 
     # To run the old setup action which is javascript
     - name: Setup Node