do_cmake.sh: use python-3.9 with fedora version 33

Fedora-33 (rawhide) now has python-3.9.
Build breaks on Fedoa-33 with Traceback:
CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:165 (message):
  Could NOT find Python3: Found unsuitable version "3.9.0", but required is
  exact version "3.8" (found /usr/bin/python3, found components: Interpreter
  Development)

Fixes: https://tracker.ceph.com/issues/47971
Signed-off-by: Sunny Kumar <sunkumar@redhat.com>

do_cmake.sh

@@ -17,8 +17,10 @@ if [ -r /etc/os-release ]; then
   case "$ID" in
       fedora)
           PYBUILD="3.7"
-          if [ "$VERSION_ID" -ge "32" ] ; then
+          if [ "$VERSION_ID" -eq "32" ] ; then
               PYBUILD="3.8"
+          elif [ "$VERSION_ID" -ge "33" ] ; then
+              PYBUILD="3.9"
           fi
           ;;
       rhel|centos)