flake check: propagate nix flake check failure as a non-zero nina exit code instead of always returning 0; bump v3.4.13

@@ -1 +1 @@1-3.4.121+3.4.13

@@ -1699,7 +1699,11 @@16991699     if (std.mem.eql(u8, ctx.sub, "check")) {17001700         output.flakeCheckStart();17011701         const code = try exec.flakeCheck(ctx.io, &ctx.machine, ctx.gpa, ctx.passthrough);1702-        if (code == 0) output.flakeValid() else output.checkFailed("");1702+        if (code != 0) {1703+            output.checkFailed("");1704+            return error.CheckFailed;1705+        }1706+        output.flakeValid();17031707         return;17041708     }17051709     if (std.mem.eql(u8, ctx.sub, "show")) {

@@ -187,6 +187,8 @@187187     switch (err) {188188         // abort message already printed by output.aborted() — just exit non-zero189189         error.HookAborted => {},190+        // "config invalid" already printed by output.checkFailed() — just exit non-zero191+        error.CheckFailed => {},190192         error.BuildFailed => {191193             const stderr = errors.getBuildStderr();192194             const translated = errors.translateError(allocator, stderr);