ci: Corrected TEST_DATA_DIR for windows

Author: Jaskowicz1

.github/workflows/ci.yml

@@ -247,6 +247,8 @@ jobs:
       - name: Run offline unit tests
         if: ${{ matrix.cfg.unittest }}
         run: cd main\build\library\${{matrix.cfg.config}} && .\unittest.exe | cat output.txt
+        env:
+          TEST_DATA_DIR: '${{github.workspace}}\testdata\'
 
       - name: Print Unit Test logs
         if: ${{ matrix.cfg.unittest && (success() || failure()) }}