Fix docs generation
Fixes the following build error:
[ 193s] + /usr/bin/make docs docker-docs
[ 193s] hack/markdown-preprocess
[ 193s] if [ ! -x "./test/tools/build/go-md2man" ]; then \
[ 193s] /usr/bin/make -C test/tools build/go-md2man GOOS=linux GOARCH=amd64; \
[ 193s] fi
[ 193s] make[1]: Entering directory '/home/abuild/debbuild/BUILD/podman-4.8.0/test/tools'
[ 193s] go build -o build/go-md2man ./vendor/github.com/cpuguy83/go-md2man/v2
[ 193s] vendor/github.com/cpuguy83/go-md2man/v2/md2man.go:9:2: cannot find package "github.com/cpuguy83/go-md2man/v2/md2man" in any of:
[ 193s] /usr/lib/go-1.21/src/github.com/cpuguy83/go-md2man/v2/md2man (from $GOROOT)
[ 193s] /home/abuild/debbuild/BUILD/podman-4.8.0/gvisor-tap-vsock-db608827124caa71ba411cec8ea959bb942984fe/_build/src/github.com/cpuguy83/go-md2man/v2/md2man (from $GOPATH)
[ 193s] /home/abuild/debbuild/BUILD/podman-4.8.0/gvisor-tap-vsock-db608827124caa71ba411cec8ea959bb942984fe/src/github.com/cpuguy83/go-md2man/v2/md2man
[ 193s] make[1]: *** [Makefile:31: build/go-md2man] Error 1
[ 193s] make[1]: Leaving directory '/home/abuild/debbuild/BUILD/podman-4.8.0/test/tools'
[ 193s] make: *** [Makefile:958: .install.md2man] Error 2