In CI, separate OS name from runner version

In the matrix config, separate the notions of "os.name" (the nice name
shown in the CI GUI) from "os.runs_on" (the value used for selecting the
runner).

They are still aligned after this change, but can now be manipulated
independently.

Author: sirosen

.github/workflows/ci.yml

@@ -303,16 +303,19 @@ jobs:
     uses: ./.github/workflows/reusable-qa.yml
 
   test:
-    name: ${{ matrix.os }} / ${{ matrix.python-version }} / ${{ matrix.pip-version }}
-    runs-on: ${{ matrix.os }}-latest
+    name: ${{ matrix.os.name }} / ${{ matrix.python-version }} / ${{ matrix.pip-version }}
+    runs-on: ${{ matrix.os.runs_on }}
     timeout-minutes: 15
     strategy:
       fail-fast: false
       matrix:
         os:
-          - Ubuntu
-          - Windows
-          - macOS
+          - name: Ubuntu
+            runs_on: ubuntu-latest
+          - name: Windows
+            runs_on: windows-latest
+          - name: macOS
+            runs_on: macos-latest
         python-version: >-
           ${{
             fromJSON(
@@ -420,26 +423,29 @@ jobs:
           flags: >-
             CI-GHA,
             OS-${{ runner.os }},
-            VM-${{ matrix.os }},
+            VM-${{ matrix.os.name }},
             Py-${{ steps.python-install.outputs.python-version }},
             Pip-${{ matrix.pip-version }}
           name: >-
             OS-${{ runner.os }},
-            VM-${{ matrix.os }},
+            VM-${{ matrix.os.name }},
             Py-${{ steps.python-install.outputs.python-version }},
             Pip-${{ matrix.pip-version }}
 
   pypy:
-    name: ${{ matrix.os }} / ${{ matrix.python-version }} / ${{ matrix.pip-version }}
-    runs-on: ${{ matrix.os }}-latest
+    name: ${{ matrix.os.name }} / ${{ matrix.python-version }} / ${{ matrix.pip-version }}
+    runs-on: ${{ matrix.os.runs_on }}
     timeout-minutes: 9
     strategy:
       fail-fast: false
       matrix:
         os:
-          - Ubuntu
-          - MacOS
-          - Windows
+          - name: Ubuntu
+            runs_on: ubuntu-latest
+          - name: MacOS
+            runs_on: macos-latest
+          - name: Windows
+            runs_on: windows-latest
         python-version:
           - pypy-3.10
         pip-version: