Wrap condition in ${{ }}

As @dantti suggested, it's a good habit to wrap the condition in ${{}}
as e.g. the negation mark (!) is a special YAML character and if there's
a problem with the tested variable it may evaluate to weird stuff and
be hard to debug. Let's be defensive.

.github/workflows/build.yml

@@ -32,7 +32,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Install ninja-build tool
-        if: runner.os != 'Linux'
+        if: ${{ runner.os != 'Linux' }}
         uses: turtlesec-no/get-ninja@main
 
       - name: Make sure MSVC is found when Ninja generator is in use