Compare matrix.generator with '-G Ninja'

The new matrix.generator value is "-G Ninja", so matrix.generator should
be compared with '-G Ninja' instead of 'Ninja'.

.github/workflows/ci-windows.yml

diff --git a/.github/workflows/ci-windows.yml b/.github/workflows/ci-windows.yml
index 0b534f8..1647a10 100644
--- a/.github/workflows/ci-windows.yml
+++ b/.github/workflows/ci-windows.yml
@@ -71,11 +71,11 @@
         working-directory: ./build
         run: ctest -C Release -j $Env:NUMBER_OF_PROCESSORS --output-on-failure
       - name: Set the config folder for Ninja
-        if: ${{ matrix.generator == 'Ninja' }}
+        if: ${{ matrix.generator == '-G Ninja' }}
         run:
           echo "CONFIG_DIR=" >> $env:GITHUB_ENV
       - name: Set the config folder for multi-config MSVC
-        if: ${{ matrix.generator != 'Ninja' }}
+        if: ${{ matrix.generator != '-G Ninja' }}
         run:
           echo "CONFIG_DIR=Release\" >> $env:GITHUB_ENV
       - name: Check static link bundling