Don't force rebuild on Windows build GH Action (#1985)

Switching `/t:ZeroTierOne:Rebuild` to just `/t:ZeroTierOne` allows the Windows build to use the rust cache.  `/t:ZeroTierOne:Rebuild` cleared the cache before building.

.github/workflows/build.yml

@@ -95,4 +95,4 @@ jobs:
       uses: microsoft/[email protected]
     - name: msbuild
       run: |
-        msbuild windows\ZeroTierOne.sln /m /p:Configuration=Release  /property:Platform=x64 /t:ZeroTierOne:Rebuild        
+        msbuild windows\ZeroTierOne.sln /m /p:Configuration=Release  /property:Platform=x64 /t:ZeroTierOne