nixosTests.gitea,nixosTests.forgejo: fix test on i686-linux

Fail pattern:
1. Unsuspecting `qemu-kvm` notice:
```
server # qemu-kvm: at most 2047 MB RAM can be simulated
```

2. Hard fail
```
    self.shell.send(out_command.encode())
BrokenPipeError: [Errno 32] Broken pipe
```

(Took me a while to consider those lines are related)

nixos/tests/gitea.nix

@@ -30,7 +30,7 @@ let
 
     nodes = {
       server = { config, pkgs, ... }: {
-        virtualisation.memorySize = 2048;
+        virtualisation.memorySize = 2047;
         services.gitea = {
           enable = true;
           database = { inherit type; };