Update PyPy to 7.3.1 on Windows.

Refs #1569

appveyor.yml

@@ -59,7 +59,7 @@ environment:
       PYTHON_EXE: python
 
     # 32-bit
-    - PYTHON: "C:\\pypy2.7-v7.2.0-win32"
+    - PYTHON: "C:\\pypy2.7-v7.3.1-win32"
       PYTHON_ID: "pypy"
       PYTHON_EXE: pypy
       PYTHON_VERSION: "2.7.x"
@@ -133,10 +133,10 @@ install:
         New-Item -ItemType directory -Path "$env:PYTMP" | Out-Null;
       }
       if ("${env:PYTHON_ID}" -eq "pypy") {
-        if (!(Test-Path "${env:PYTMP}\pypy2-v7.2.0-win32.zip")) {
-          (New-Object Net.WebClient).DownloadFile('https://bitbucket.org/pypy/pypy/downloads/pypy2.7-v7.2.0-win32.zip', "${env:PYTMP}\pypy2-v7.2.0-win32.zip");
+        if (!(Test-Path "${env:PYTMP}\pypy2-v7.3.1-win32.zip")) {
+          (New-Object Net.WebClient).DownloadFile('https://bitbucket.org/pypy/pypy/downloads/pypy2.7-v7.3.1-win32.zip', "${env:PYTMP}\pypy2-v7.3.1-win32.zip");
         }
-        7z x -y "${env:PYTMP}\pypy2-v7.2.0-win32.zip" -oC:\ | Out-Null;
+        7z x -y "${env:PYTMP}\pypy2-v7.3.1-win32.zip" -oC:\ | Out-Null;
         & "${env:PYTHON}\pypy.exe" "-mensurepip";
 
       }

docs/changes/1569.feature

+Update tested PyPy version from 7.2.0 on Windows to 7.3.1 and from
+7.3.0 to 7.3.1 on Linux and macOS.