.github: test cygwin cache

Author: khancyr

.github/workflows/cygwin_build.yml

@@ -174,6 +174,7 @@ jobs:
           echo "export CCACHE_COMPRESS=1" >> ~/ccache.conf &&
           echo "export CCACHE_COMPRESSLEVEL=6" >> ~/ccache.conf &&
           echo "export CCACHE_MAXSIZE=400M" >> ~/ccache.conf &&
+          echo "export CCACHE_UMASK=002" >> ~/ccache.conf &&
           source ~/ccache.conf &&
           ccache -s
       - name: ccache cache files