ci/ga: Simplify documentaitons ci jobs (#2957)

Print the used OS image in the job name.
Generate the base vs. head job matrix dimension dynamically.

.github/workflows/pnl-ci-docs.yml

@@ -17,26 +17,14 @@ concurrency:
 
 jobs:
   docs-build:
-    # Python 3.7 x64 on macos-14 (arm64) images is broken [0]
-    # and arm64 version is not available [1].
-    # Restrict python 3.7 macos runs to macos-13
-    # [0] https://github.com/actions/setup-python/issues/855
-    # [1] https://github.com/actions/setup-python/issues/856
-    runs-on: ${{ (matrix.os == 'macos-latest' && matrix.python-version == '3.7') && 'macos-13' || matrix.os }}
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
-      # Matrix setup is a hacky way to include 'base' build in pull requests
-      # The entire matrix is set up and 'base' builds are pruned based
-      # on event name and final configuration (ubuntu, python3.11).
       matrix:
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
         os: [ubuntu-latest, macos-latest, windows-latest]
-        event:
-          - ${{ github.event_name }}
-        pnl-version: ['head', 'base']
+        pnl-version: ${{ (github.event_name == 'push') && fromJSON('["head"]') || fromJSON('["head", "base"]') }}
         exclude:
-          - event: 'push'
-            pnl-version: 'base'
           - os: macos-latest
             pnl-version: 'base'
           - os: windows-latest
@@ -50,6 +38,19 @@ jobs:
           - python-version: '3.10'
             pnl-version: 'base'
 
+            # Python 3.7 x64 on macos-14 (arm64) images is broken [0]
+            # and arm64 version is not available [1].
+            # Restrict python 3.7 macos runs to macos-13
+            # [0] https://github.com/actions/setup-python/issues/855
+            # [1] https://github.com/actions/setup-python/issues/856
+          - python-version: '3.7'
+            os: macos-latest
+
+        include:
+          - python-version: '3.7'
+            os: macos-13
+            pnl-version: 'head'
+
     outputs:
       on_master: ${{ steps.on_master.outputs.on-branch }}