Use working directory step option instead of explicit "cd"

This seems simpler and more explicit ("cd" is easy to miss or forget).

.github/workflows/ci.yml

@@ -91,9 +91,9 @@ jobs:
           echo SWIGJOBS=-j$cpu_count >> $GITHUB_ENV
 
     - name: build
+      working-directory: build/build
       run: |
           set -x
-          cd ${GITHUB_WORKSPACE}/build/build;
           make -s $SWIGJOBS
           ./swig -version && ./swig -pcreversion
           if test -z "$SWIGLANG"; then make -s $SWIGJOBS check-ccache; fi
@@ -101,9 +101,9 @@ jobs:
           echo 'Installing...'
           if test -z "$SWIGLANG"; then sudo make -s install && swig -version && ccache-swig -V; fi
     - name: tests
+      working-directory: build/build
       run: |
           set -x
-          cd ${GITHUB_WORKSPACE}/build/build;
           if test -n "$CPP11"; then export CPPSTD=c++11; fi
           if test -n "$CPP14"; then export CPPSTD=c++14; fi
           if test -n "$CPP17"; then export CPPSTD=c++17; fi