[eric] ci: add a windows-2019 (win10-era kernel) runner to the e2e matrix so older windows is covered too

.github/workflows/e2e.yml

@@ -19,7 +19,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [windows-latest, macos-latest]
+        # windows-latest = Win Server 2022 (NT 10.0.20348, Win11-era); windows-2019
+        # = NT 10.0.17763 (Win10 1809 kernel) for older-Windows coverage; macos-latest
+        # for the DMG. GitHub has no Win10-client image, so 2019 is the closest proxy.
+        os: [windows-latest, windows-2019, macos-latest]
     runs-on: ${{ matrix.os }}
     timeout-minutes: 90
     env:
@@ -39,12 +42,12 @@ jobs:
           python-version: '3.13'
 
       - name: Build packaged app (Windows)
-        if: matrix.os == 'windows-latest'
+        if: startsWith(matrix.os, 'windows')
         shell: pwsh
         run: pwsh -NoProfile -File scripts/build-app-win.ps1
 
       - name: Build packaged app (macOS)
-        if: matrix.os == 'macos-latest'
+        if: startsWith(matrix.os, 'macos')
         shell: bash
         run: bash scripts/build-app.sh