Avoid templating GitHub Actions workflow

GitHub Actions workflow have sufficient power to express what we need.
We don't need to maintain and additional templating solution on top.

.github/workflows/bootstrap.yml

@@ -1,10 +1,5 @@
-# This file is auto-generated
-#
-# To regenerate it run
-#
-#     make github-actions
-#
 name: Bootstrap
+
 on:
   push:
     branches:
@@ -15,37 +10,21 @@ on:
       - created
 
 jobs:
-  bootstrap-linux:
-    name: Bootstrap on Linux
-    runs-on: ubuntu-18.04
-    steps:
-      - uses: actions/checkout@v2
-      - name: bootstrap.py
-        run: |
-          ghcup config set cache true
-          ghcup install ghc 8.10.7
-          python3 bootstrap/bootstrap.py -w $(ghcup whereis ghc 8.10.7) -d bootstrap/linux-8.10.7.json
-
-      - name: Smoke test
-        run: |
-          _build/bin/cabal --version
-
-      - uses: actions/upload-artifact@v2
-        with:
-          name: cabal-linux-bootstrapped
-          path: _build/artifacts/*
-
-  bootstrap-macos:
-    name: Bootstrap on macOS
-    runs-on: macos-latest
+  bootstrap:
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+    name: Bootstrap ${{ matrix.os }}
+    runs-on: $${ matrix.os }}
     steps:
       - uses: actions/checkout@v2
-
-      # We use linux dependencies
       - name: bootstrap.py
         run: |
           ghcup config set cache true
           ghcup install ghc 8.10.7
+          # We use linux dependencies also on macos
           python3 bootstrap/bootstrap.py -w $(ghcup whereis ghc 8.10.7) -d bootstrap/linux-8.10.7.json
 
       - name: Smoke test
@@ -54,5 +33,5 @@ jobs:
 
       - uses: actions/upload-artifact@v2
         with:
-          name: cabal-macos-bootstrapped
+          name: cabal-${{ matrix.os }}-bootstrapped
           path: _build/artifacts/*