bpo-47138: Ensure Windows docs build uses the same pinned version as other platforms (GH-32161)

Author: zooba

Doc/make.bat

@@ -13,7 +13,7 @@ if not defined SPHINXBUILD (
     %PYTHON% -c "import sphinx" > nul 2> nul
     if errorlevel 1 (
         echo Installing sphinx with %PYTHON%
-        %PYTHON% -m pip install sphinx==2.2.0
+        %PYTHON% -m pip install -r requirements.txt
         if errorlevel 1 exit /B
     )
     set SPHINXBUILD=%PYTHON% -c "import sphinx.cmd.build, sys; sys.exit(sphinx.cmd.build.main())"
@@ -30,6 +30,7 @@ if not defined BLURB (
     %PYTHON% -c "import blurb" > nul 2> nul
     if errorlevel 1 (
         echo Installing blurb with %PYTHON%
+        rem Should have been installed with Sphinx earlier
         %PYTHON% -m pip install blurb
         if errorlevel 1 exit /B
     )
@@ -40,6 +41,7 @@ if not defined SPHINXLINT (
     %PYTHON% -c "import sphinxlint" > nul 2> nul
     if errorlevel 1 (
         echo Installing sphinx-lint with %PYTHON%
+        rem Should have been installed with Sphinx earlier
         %PYTHON% -m pip install sphinx-lint
         if errorlevel 1 exit /B
     )