Setting BDS appears to be needed as well.

.github/workflows/build.yml

@@ -33,7 +33,8 @@ jobs:
           Remove-Item issrc-build-env.zip
           $DELPHIXEROOT = (Get-Item .\issrc-build-env).FullName
           "DELPHIXEROOT=$DELPHIXEROOT" | Out-File -NoNewline -Encoding ascii -Append "$env:GITHUB_ENV"
-          "set BDSCOMMONDIR=$DELPHIXEROOT" | Out-File -NoNewline -Encoding ascii issrc-build-env\bin\rsvars.bat
+          "set BDS=$DELPHIXEROOT" | Out-File -Encoding ascii issrc-build-env\bin\rsvars.bat
+          "set BDSCOMMONDIR=$DELPHIXEROOT" | Out-File -NoNewline -Encoding ascii -Append issrc-build-env\bin\rsvars.bat
       - name: Configure build
         run: |
           "set DELPHIXEROOT=$env:DELPHIXEROOT" | Out-File -Encoding ascii compilesettings.bat

.github/workflows/build2.yml

@@ -33,7 +33,8 @@ jobs:
           Remove-Item issrc-build-env.zip
           $DELPHIXEROOT = (Get-Item .\issrc-build-env).FullName
           "DELPHIXEROOT=$DELPHIXEROOT" | Out-File -NoNewline -Encoding ascii -Append "$env:GITHUB_ENV"
-          "set BDSCOMMONDIR=$DELPHIXEROOT" | Out-File -NoNewline -Encoding ascii issrc-build-env\bin\rsvars.bat
+          "set BDS=$DELPHIXEROOT" | Out-File -Encoding ascii issrc-build-env\bin\rsvars.bat
+          "set BDSCOMMONDIR=$DELPHIXEROOT" | Out-File -NoNewline -Encoding ascii -Append issrc-build-env\bin\rsvars.bat
       - name: Configure build
         run: |
           "set DELPHIXEROOT=$env:DELPHIXEROOT" | Out-File -Encoding ascii compilesettings.bat