ci: debug (wip) try to prevent gc with nix profiles

.forgejo/workflows/check.yml

@@ -32,7 +32,7 @@ jobs:
             cache-${{ runner.os }}-nix-store-
 
           gc-linux: true
-          gc-max-store-size-linux: 20000000000
+          gc-max-store-size-linux: 10000000000
 
           purge-caches: true
           purge-key: cache-${{ runner.os }}-nix-store-
@@ -49,3 +49,17 @@ jobs:
       - name: Run flake checks
         run: |
           nix --print-build-logs --verbose --accept-flake-config --access-tokens '' flake check
+          # Prevent cache garbage collection
+          for target in $(nix flake show --json --all-systems | jq '
+            ["nixosConfigurations"] as $tops |
+            $tops[] as $top |
+            .[$top] |
+            to_entries[] |
+            .key as $hostname |
+            .value |
+            keys[] |
+            "\($top).\($hostname).config.system.build.toplevel"
+            ' | tr -d '"'
+          ); do
+            nix profile install .#$target
+          done