build: disable PDB debug symbols in releases [CI SKIP]

backend/Directory.Build.props

@@ -5,6 +5,8 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <DebugType>none</DebugType>
+    <DebugSymbols>false</DebugSymbols>
     <AnalysisLevel>latest-recommended</AnalysisLevel>
     <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
     <InvariantGlobalization>true</InvariantGlobalization>