Use PEP 503 names for BuildRequires

Since Fedora 33, we generate both python3dist(foo.bar) and python3dist(foo-bar)
provides, but we'd like to follow PEP 503 and use only the names with dash.

By using the dashes, this is not compatible with the provides generated in EPEL 8,
compatibility can be achieved with the %py3_dist macro.

python-portend.spec

@@ -21,7 +21,7 @@ momentous or calamitous) is likely to happen.
 Summary:        portend documentation
 
 BuildRequires:  python3-devel
-BuildRequires:  python3dist(jaraco.functools)
+BuildRequires:  python3dist(jaraco-functools)
 BuildRequires:  python3dist(pytest) >= 3.4
 #BuildRequires:  python3dist(pytest-sugar) >= 0.9.1
 BuildRequires:  python3dist(setuptools)
@@ -36,8 +36,8 @@ momentous or calamitous) is likely to happen.
 %package -n python-%{pypi_name}-doc
 Summary:        portend documentation
 
-BuildRequires:  python3dist(jaraco.packaging) >= 3.2
-BuildRequires:  python3dist(rst.linker) >= 1.9
+BuildRequires:  python3dist(jaraco-packaging) >= 3.2
+BuildRequires:  python3dist(rst-linker) >= 1.9
 BuildRequires:  python3dist(sphinx)
 BuildRequires:  python3-more-itertools