make fails with No rule to make target 'SHELL'

On current Fedora, the package is failing to build with:

/usr/bin/make -f Makefile.man2html build
make[1]: *** No rule to make target 'SHELL'.  Stop.
make: *** [Makefile:88: build_man] Error 2

Removing the MAKEOVERRIDES line https://gitlab.x2go.org/x2go/client/x2goclient/-/blob/master/Makefile#L68 seems to resolve it.

See Debian bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1089277

Patch: https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=1089277;filename=x2goclient.diff.txt;msg=14