python -m pip install --upgrade pip goes into backtracking since 20.3.2

[jiasli]

Environment

• pip version: 20.3.2
• Python version: 3.8.6
• OS: Windows 10

Description
python -m pip install --upgrade pip goes into backtracking since 20.3.2.

Expected behavior
The command should succeed without going into backtracking.

How to Reproduce
Upgrade pip to the latest 20.3.2:

python -m pip install --upgrade pip

Then run it again

> python -m pip install --upgrade pip
Requirement already satisfied: pip in d:\env38-1\lib\site-packages (20.3.2)
Collecting pip
  Using cached pip-20.3.2-py2.py3-none-any.whl (1.5 MB)
  Using cached pip-20.3.2.tar.gz (1.5 MB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
    Preparing wheel metadata ... done
  Using cached pip-20.3.1-py2.py3-none-any.whl (1.5 MB)
  Using cached pip-20.3.1.tar.gz (1.5 MB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
    Preparing wheel metadata ... done
  Using cached pip-20.3-py2.py3-none-any.whl (1.5 MB)
  Using cached pip-20.3.tar.gz (1.5 MB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
    Preparing wheel metadata ... done
  Using cached pip-20.2.4-py2.py3-none-any.whl (1.5 MB)
  Using cached pip-20.2.4.tar.gz (1.5 MB)
  Installing build dependencies ... canceled
...
  Downloading pip-0.4.tar.gz (50 kB)
     |████████████████████████████████| 50 kB 3.1 MB/s
  Downloading pip-0.3.1.tar.gz (48 kB)
     |████████████████████████████████| 48 kB 3.2 MB/s
  Downloading pip-0.3.tar.gz (47 kB)
     |████████████████████████████████| 47 kB 3.4 MB/s
WARNING: Discarding https://files.pythonhosted.org/packages/17/05/f66144ef69b436d07f8eeeb28b7f77137f80de4bf60349ec6f0f9509e801/pip-0.3.tar.gz#sha256=183c72455cb7f8860ac1376f8c4f14d7f545aeab8ee7c22cd4caf79f35a2ed47 (from https://pypi.org/simple/pip/). Requested pip from https://files.pythonhosted.org/packages/17/05/f66144ef69b436d07f8eeeb28b7f77137f80de4bf60349ec6f0f9509e801/pip-0.3.tar.gz#sha256=183c72455cb7f8860ac1376f8c4f14d7f545aeab8ee7c22cd4caf79f35a2ed47 has different version in metadata: '0.3.dev0'
  Downloading pip-0.2.1.tar.gz (39 kB)
  Downloading pip-0.2.tar.gz (38 kB)

It takes very long to finish.

[ryboe]

dup of #9284