Fixed pip backtracking for coverage package

Signed-off-by: Andreas Maier <[email protected]>

dev-requirements.txt

@@ -56,7 +56,10 @@ packaging>=21.0,<22.0
 colorama>=0.4.5
 
 # Coverage reporting (no imports, invoked via coveralls script):
-coverage>=5.5
+# coveralls pins coverage to <7.0, causing pip backtracking to happen. Pinning
+# it to <7.0 in this file saves the time for backtracking, but requires to
+# occasionally check for new versions of coveralls without pinning.
+coverage>=5.5,<7.0
 pytest-cov>=2.12.1
 coveralls>=3.3.0