upgrade-nix: use --store local, so we don't kill our own access to the daemon

Tested in a Debian container.

Fixes #1189
Fixes https://git.lix.systems/lix-project/lix-installer/issues/79

Change-Id: Id7de28bf81eb122dd60755622b7816716a6a6964

lix/nix/upgrade-nix.cc

@@ -141,6 +141,8 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
             // install the new one, in case the new and old versions aren't considered
             // to be "the same package" by nix-env's logic (e.g., if their pnames differ).
             Strings removeArgs = {
+                "--store",
+                "local",
                 "--uninstall",
                 oldNixEnv,
                 "--profile",
@@ -150,6 +152,8 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
             aio().blockOn(runProgram(newNixEnv, false, removeArgs));
 
             Strings upgradeArgs = {
+                "--store",
+                "local",
                 "--profile",
                 this->profileDir,
                 "--install",

misc/upgrade-lix.sh

@@ -124,9 +124,12 @@ checkSystemdService
 
 set -x
 exec "$NIX" run \
+    --store local \
     --extra-experimental-features "nix-command flakes" \
     "${SUBSTITUTER_ARGS[@]}" \
     "${LIX_BASE}?ref=${LIX_REF}" \
+    -- \
+    --store local \
     --extra-experimental-features "nix-command flakes" \
     upgrade-nix \
     "${SUBSTITUTER_ARGS[@]}"