Move the .NET Runtime flag into a variable

debian/rules

@@ -2,6 +2,7 @@
 CONFIG := Release
 TERM := xterm
 SHELL := /bin/bash
+DOTNETRUNTIME := linux-x64
 export DH_VERBOSE=1
 export DOTNET_CLI_TELEMETRY_OPTOUT=1
 
@@ -15,7 +16,7 @@ override_dh_auto_test:
 override_dh_clistrip:
 
 override_dh_auto_build:
-	dotnet publish --configuration $(CONFIG) --output='$(CURDIR)/usr/lib/jellyfin/bin' --self-contained --runtime linux-x64
+	dotnet publish --configuration $(CONFIG) --output='$(CURDIR)/usr/lib/jellyfin/bin' --self-contained --runtime $(DOTNETRUNTIME)
 
 override_dh_auto_clean:
 	dotnet clean -maxcpucount:1 --configuration $(CONFIG) || true