fix Nushell tests (!24)

because this was developed when Nushell was in 0.95.0, some tweaks had to be added

- allow to set the Nushell binary with the `NU` var in `Makefile`, e.g. `make NU="nu-0.95.0" test` if you have Nushell 0.95.0 installed as `nu-0.95.0` in `PATH`
- use `$nu.current-exe` for nested Nushell invocation to preserve the version set in the top-level `Makefile`
- use `--no-config-file` to make sure there is no interaction with the user's config, which might not be for the correct version

Makefile

+NU="nu"
 .PHONY: fmt fmt-check check clippy test show show-proxy unset-proxy toto
 
 ssh_addr_file = 0
@@ -19,9 +20,9 @@ clippy:
 test:
 	cargo build --release
 ifeq ($(ssh_addr_file),0)
-	nu help_func/execute_all_tests.nu
+	${NU} --no-config-file help_func/execute_all_tests.nu
 else
-	nu help_func/execute_all_tests.nu --ssh-addr-file $(ssh_addr_file)
+	${NU} --no-config-file help_func/execute_all_tests.nu --ssh-addr-file $(ssh_addr_file)
 endif
 
 show:
@@ -30,7 +31,7 @@ show:
 	rustc --version
 	cargo --version
 	cargo clippy --version
-	nu --version
+	${NU} --version
 
 show-proxy:
 	@echo "HTTP_PROXY = ${HTTP_PROXY}"

help_func/execute_all_tests.nu

@@ -13,9 +13,9 @@ def main [--ssh-addr-file: path] {
         print $"\n(ansi yellow_reverse)    LAUNCHING TEST ($test_name)(ansi reset)\n"
 
         (if $ssh_addr_file == null {
-            nu $test_name
+            ^$nu.current-exe --no-config-file $test_name
         } else {
-            nu $test_name --ssh-addr-file=$ssh_addr_file
+            ^$nu.current-exe --no-config-file $test_name --ssh-addr-file=$ssh_addr_file
         }) e>| do { |e| # capture the possible error and check if it's empty or not
         let maybe_error = ($e | parse -r "(Error: .*)")
             if ($maybe_error | is-empty) {