Add beta suffix to local dev version

Directory.Build.props now produces 1.0.0-beta for local dev builds.
CI and NuGet release workflows pass explicit /p:Version= overrides
and are unaffected. Release tags (vMAJOR.MINOR.PATCH.REVISION[-prerelease])
already support prerelease suffixes via the existing workflow regex.

Author: PortaSFTPServer

Directory.Build.props

@@ -1,7 +1,8 @@
 <Project>
   <PropertyGroup>
     <VersionPrefix>1.0.0</VersionPrefix>
-    <Version Condition="'$(Version)' == ''">$(VersionPrefix)</Version>
+    <VersionSuffix>beta</VersionSuffix>
+    <Version Condition="'$(Version)' == ''">$(VersionPrefix)-$(VersionSuffix)</Version>
     <PackageVersion Condition="'$(PackageVersion)' == ''">$(Version)</PackageVersion>
     <RepositoryUrl>https://github.com/PortaSFTPServer/ApacheMinaSSHD.NET</RepositoryUrl>
     <RepositoryType>git</RepositoryType>