Circumvent new pip check (see pypa/pip#9628)

Author: flying-sheep

.azure-pipelines.yml

@@ -23,6 +23,7 @@ jobs:
 
   - script: |
       python -m pip install --upgrade pip
+      pip install -r .pip-2033.txt
       pip install pytest-cov wheel
       pip install .[dev,test]
     displayName: 'Install dependencies'

.pip-2033.txt

@@ -0,0 +1,4 @@
+# Flit mangles the +local part of the version spec in compliance with PEP 427,
+# but pip 20.3.4 started expecting wheel filenames to contain the local part unmangled.
+# https://github.com/pypa/pip/issues/9628
+pip==20.3.3

.readthedocs.yml

@@ -6,6 +6,7 @@ sphinx:
 python:
   version: 3.6
   install:
+  - requirements: .pip-2033.txt
   - method: pip
     path: .
     extra_requirements:

.travis.yml

@@ -17,6 +17,7 @@ python:
 - "3.6"
 - "3.7"
 install:
+- pip install -r .pip-2033.txt
 - pip install .[dev,test]
 script:
 - pytest --cov=. --cov-report=xml