osu-lazer: fix update.sh script

Use the currently checked out nixpkgs, not the system one.
Also add a CLI flag to not update the app, but dependencies only.

pkgs/games/osu-lazer/update.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p curl jq common-updater-scripts nuget-to-nix dotnet-sdk
+#!nix-shell -I nixpkgs=../../../. -i bash -p curl jq common-updater-scripts nuget-to-nix dotnet-sdk
 set -eo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
@@ -13,7 +13,11 @@ if [[ "$new_version" == "$old_version" ]]; then
 fi
 
 cd ../../..
-update-source-version osu-lazer "$new_version"
+
+if [[ "$1" != "--deps-only" ]]; then
+    update-source-version osu-lazer "$new_version"
+fi
+
 store_src="$(nix-build . -A osu-lazer.src --no-out-link)"
 src="$(mktemp -d /tmp/osu-src.XXX)"
 echo "Temp src dir: $src"
@@ -26,6 +30,7 @@ export DOTNET_NOLOGO=1
 export DOTNET_CLI_TELEMETRY_OPTOUT=1
 
 mkdir ./nuget_tmp.packages
+dotnet --info
 dotnet restore osu.Desktop --packages ./nuget_tmp.packages --runtime linux-x64
 
 nuget-to-nix ./nuget_tmp.packages > "$deps_file"