Fixed dependency error with importlib-metadata on Python 3.8

Details:

* Since today, virtualenv failed with:
    AttributeError: 'Context' object has no attribute 'pattern'
  causing the installtest to fail.

  It turned out that uninstalling the importlib-metadata package solved the
  problem. That package was stated in our requirements files to be needed by
  tox 3.14 on Python <= 3.8. However, on Python 3.8 it is already in the base
  Python and not needed as a package. Uninstalling importlib-metadata solved
  the problem. It turned out that tox 3.x requires importlib-metadata only on
  Python < 3.8. It is not clear why this error showed up only starting today.
  Searching for packages released today (2021-07-18) did not reveal anything.

  This change fixes the problem by changing python_version <= '3.8' to < '3.8'
  on importlib-metadata inthe requirements files.

Signed-off-by: Andreas Maier <andreas.r.maier@gmx.de>

dev-requirements.txt

@@ -42,8 +42,8 @@ PyYAML>=5.3.1; python_version > '3.4'
 # Tox
 tox>=2.5.0
 # tox 3.17 requires six>=1.14.0 - covered in test-requirements.txt
-# tox 3.14 requires importlib-metadata<1,>=0.12 on py<=3.8
-importlib-metadata<1,>=0.12; python_version <= '3.8'
+# tox 3.14 requires importlib-metadata<1,>=0.12 on py<3.8
+importlib-metadata<1,>=0.12; python_version < '3.8'
 
 # Sphinx (no imports, invoked via sphinx-build script):
 # Keep in sync with rtd-requirements.txt

docs/changes.rst

@@ -21,6 +21,9 @@ Released: not yet
 
 * Fixed issues raised by new Pylint 2.9.
 
+* Fixed a dependency error that caused importlib-metadata to be installed on
+  Python 3.8, while it is included in the Python base.
+
 **Enhancements:**
 
 **Cleanup:**

minimum-constraints.txt

@@ -157,8 +157,8 @@ PyYAML==5.3.1; python_version >= '3.5'
 # Tox
 tox==2.5.0
 # tox 3.17 requires six>=1.14.0
-# tox 3.14 requires importlib-metadata<1,>=0.12 on py<=3.8
-importlib-metadata==0.12; python_version <= '3.8'
+# tox 3.14 requires importlib-metadata<1,>=0.12 on py<3.8
+importlib-metadata==0.12; python_version < '3.8'
 
 # Sphinx (no imports, invoked via sphinx-build script):
 Sphinx==1.7.6