install pkgconfig in freebsd test

Author: phlptp

.github/workflows/freebsd.yml

@@ -18,10 +18,11 @@ jobs:
       with:
         usesh: true
         prepare: |
-          pkg install -y devel/googletest gcc cmake
+          pkg install -y devel/googletest cmake pkgconf
 
         run: |
           cmake -S . -B build \
+          -DCMAKE_CXX_STANDARD=17 \
           -DUNITS_ENABLE_TESTS=ON \
           -DUNITS_USE_EXTERNAL_GTEST=ON
           cmake --build build -j4