chore(workaround,test): pin coverage to <=7.6.4

Underlying issue is with 7.6.5: reported to
nedbat/coveragepy#1891 . First 7.6.1 was tried
and it worked. Next bisection is 7.6.3 was ok.
nedbat clarified that indeed in 7.6.5 some assertions were added:
nedbat/coveragepy#1891 (comment)

So we will just keep it that ceiled until issue resolved.

setup.py

@@ -87,7 +87,8 @@
     ],
     'devel-utils': [
         'asv',        # benchmarks
-        'coverage',
+        # https://github.com/nedbat/coveragepy/issues/1891#issuecomment-2477760029
+        'coverage<=7.6.4',
         'gprof2dot',  # rendering cProfile output as a graph image
         'psutil',
         'pytest-xdist',  # parallelize pytest runs etc