add BuildRequires: perl-generators

[Fuchange]

When I build pakcages on a minimal Centos8 ,I built it successfully， but the built package lacks some providers

# rpm -qp --provides perl-Test-LongString-0.17-1.el8.noarch.rpm
perl-Test-LongString = 0.17-1.el8

It made me unable to build perl-Test-Nginx because I dont have any package can provided perl(Test::LongString) on my local repo.

The same problems at perl-Readonly and perl-Test-Simple.

So I add BuildRequires: perl-generators at perl-Readonly.spec perl-Test-LongString.spec perl-Test-Simple.spec .

and then

# rpm -qp --provides perl-Test-LongString-0.17-1.el8.noarch.rpm
perl(Test::LongString) = 0.17
perl-Test-LongString = 0.17-1.el8

it's works~

Of course, it can be solved like commit b6b0c78a, depending on your opinion～