cirrus: update to python38 on FreeBSD test cases

py37-sphinx is not available anymore on freebsd-12-2 and freebsd-11-4.

Author: xdelaruelle

.cirrus.yml

@@ -88,7 +88,7 @@ task:
       image_family: freebsd-12-2
     cpu: 1
     memory: 2G
-  reqinstall_script: pkg install -y bash wget gmake dejagnu py37-sphinx tcl86 tcl-wrapper autoconf automake gettext ksh93 zsh fish perl5 python37 ruby cmake R readline
+  reqinstall_script: pkg install -y bash wget gmake dejagnu py38-sphinx tcl86 tcl-wrapper autoconf automake gettext ksh93 zsh fish perl5 python38 ruby cmake R readline
   configure_script:
     - ./configure --enable-compat-version --without-tclx --with-tcl-ver=8.6
   << : *BUILD_INSTALL_TEST_TEMPLATE