bpo-31569: correct PCBuild/ case to PCbuild/ in build scripts and docs (GH-3711)

diff --git a/Tools/msi/wix.props b/Tools/msi/wix.props
index fbb2d10..7269d34 100644
--- a/Tools/msi/wix.props
+++ b/Tools/msi/wix.props
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="..\..\PCBuild\python.props" />
+  <Import Project="..\..\PCbuild\python.props" />
   
   <PropertyGroup>
     <WixInstallPath Condition="'$(WixInstallPath)' == '' and Exists('$(MSBuildThisFileDirectory)\Wix')">$(MSBuildThisFileDirectory)\Wix\</WixInstallPath>