nix: only use stable commands

Avoid the following error when installing nix-unstable:

    experimental Nix feature 'nix-command' is disabled; use '--experimental-features nix-command' to override

dist/main/index.js

@@ -1072,7 +1072,7 @@ function setup() {
                 core.exportVariable('CACHIX_SIGNING_KEY', signingKey);
             }
             // Remember existing store paths
-            yield exec.exec("sh", ["-c", `nix path-info --all | grep -v '\.drv$' > /tmp/store-path-pre-build`]);
+            yield exec.exec("sh", ["-c", `${__dirname}/list-nix-store.sh > /tmp/store-path-pre-build`]);
         }
         catch (error) {
             core.setFailed(`Action failed with error: ${error}`);

dist/main/list-nix-store.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# Small utility to replace `nix path-info --all`
+set -euo pipefail
+
+for file in /nix/store/*; do
+  case "$file" in
+  *.drv)
+    # Avoid .drv as they are not generally useful
+    continue
+    ;;
+  *.check)
+    # Skip .check file produced by --keep-failed
+    continue
+    ;;
+  *)
+    echo "$file"
+    ;;
+  esac
+done

dist/main/push-paths.sh

@@ -1,4 +1,4 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-comm -13 <(sort /tmp/store-path-pre-build) <(nix path-info --all | grep -v '\.drv$' | sort) | $1 push -j8 $2
+comm -13 <(sort /tmp/store-path-pre-build) <("$(dirname "$0")"/list-nix-store.sh) | "$1" push -j8 "$2"