bpo-33522: Enable CI builds on Visual Studio Team Services (GH-6865) (GH-6926)

(cherry picked from commit e5f41d2f1e0b8b8e61d5fa427c19bd1ea90fd9a3)

Co-authored-by: Steve Dower <steve.dower@microsoft.com>
diff --git a/Doc/make.bat b/Doc/make.bat
index 3f201de..c69cfae 100644
--- a/Doc/make.bat
+++ b/Doc/make.bat
@@ -6,17 +6,20 @@
 set this=%~n0
 
 call ..\PCbuild\find_python.bat %PYTHON%
-if not defined SPHINXBUILD if defined PYTHON (
+
+if not defined PYTHON set PYTHON=py
+
+if not defined SPHINXBUILD (
     %PYTHON% -c "import sphinx" > nul 2> nul
     if errorlevel 1 (
         echo Installing sphinx with %PYTHON%
-        %PYTHON% -m pip install sphinx
+        %PYTHON% -m pip install sphinx python-docs-theme
         if errorlevel 1 exit /B
     )
     set SPHINXBUILD=%PYTHON% -c "import sphinx, sys; sys.argv[0] = 'sphinx-build'; sphinx.main()"
 )
 
-if not defined BLURB if defined PYTHON (
+if not defined BLURB (
     %PYTHON% -c "import blurb" > nul 2> nul
     if errorlevel 1 (
         echo Installing blurb with %PYTHON%
@@ -26,7 +29,6 @@
     set BLURB=%PYTHON% -m blurb
 )
 
-if not defined PYTHON set PYTHON=py
 if not defined SPHINXBUILD set SPHINXBUILD=sphinx-build
 if not defined BLURB set BLURB=blurb