Ensure dnx run succeeds even on Windows

For some reason, default bash doesn't pick up the new dnx tool on .NET 10 under Windows.

Author: kzu

.github/workflows/build.yml

@@ -72,6 +72,7 @@ jobs:
         run: dotnet build -m:1 -bl:build.binlog
 
       - name: 🧪 test
+        shell: pwsh
         run: dnx --yes retest -- --no-build
 
       - name: 🐛 logs

.github/workflows/publish.yml

@@ -34,6 +34,7 @@ jobs:
         run: dotnet build -m:1 -bl:build.binlog
 
       - name: 🧪 test
+        shell: pwsh
         run: dnx --yes retest -- --no-build
 
       - name: 🐛 logs