Adapt %%py_dist_name to keep square brackets

So %{py3_dist foo[bar]} works as expected.

Add tests.

macros.python-srpm

@@ -70,7 +70,7 @@
 # Converts Python dist name to a canonical format
 %py_dist_name() %{lua:\
         name = rpm.expand("%{?1:%{1}}");\
-        canonical = string.gsub(string.lower(name), "%W+", "-");\
+        canonical = string.gsub(string.lower(name), "[^%w%[%]]+", "-");\
         print(canonical);\
 }