Replace old SHA1 signing certificates with SHA256 ones

Per policy we should stop using SHA1 certificates for signing binaries
and installers. The replacement for the 'Microsoft' Authenticode
certificate is 'Microsoft400'.

Author: mjcheetham

src/osx/SignFiles.Mac/SignFiles.Mac.csproj

@@ -24,7 +24,7 @@
       $(OutDir)\GitHub.dll;
       $(OutDir)\Microsoft.AzureRepos.dll;
       $(OutDir)\Microsoft.Git.CredentialManager.dll;">
-      <Authenticode>Microsoft</Authenticode>
+      <Authenticode>Microsoft400</Authenticode>
       <InProject>false</InProject>
     </FilesToSign>
     <MacFilesToSign Include="

src/windows/Installer.Windows/Installer.Windows.csproj

@@ -30,7 +30,7 @@
   <Target Name="CreateFilesToSignItems" DependsOnTargets="GetBuildVersion" BeforeTargets="PrepareForRun">
     <ItemGroup>
       <FilesToSign Include="$(OutDir)gcmcore-windows-$(BuildVersion).exe">
-        <Authenticode>Microsoft</Authenticode>
+        <Authenticode>Microsoft400</Authenticode>
         <InProject>false</InProject>
       </FilesToSign>
     </ItemGroup>

src/windows/Payload.Windows/Payload.Windows.csproj

@@ -29,7 +29,7 @@
       $(OutDir)Microsoft.AzureRepos.dll;
       $(OutDir)Microsoft.Git.CredentialManager.dll;
       $(OutDir)Microsoft.Authentication.Helper.exe;">
-      <Authenticode>Microsoft</Authenticode>
+      <Authenticode>Microsoft400</Authenticode>
       <InProject>false</InProject>
     </FilesToSign>
   </ItemGroup>