[testscripts] update to use versioned packages (#1303)

## Summary

Updating these to use versioned packages. I decided against adding
complexity to the tests by keeping unversioned packages as well, but let
me know if you disagree.

## How was it tested?

the Github Action for testscripts should pass

Author: savil

testscripts/run/env.test.txt

@@ -49,7 +49,7 @@ stdout 'devbox-json-override'
 
 -- devbox.json --
 {
-  "packages": ["nginx"],
+  "packages": ["nginx@latest"],
   "env": {
     "CONFIG_VAR1": "abc",
     "CONFIG_VAR2": "$DEVBOX_FOO",

testscripts/run/pure.test.txt

@@ -14,7 +14,7 @@ stdout 'Hello, world!'
 
 -- devbox.json --
 {
-  "packages": ["hello"],
+  "packages": ["hello@latest"],
   "env": {
     "FOO": "baz"
   }

testscripts/run/script.test.txt

@@ -28,7 +28,7 @@ stdout 'directly'
 -- devbox.json --
 {
   "packages": [
-    "hello"
+    "hello@latest"
   ],
   "shell": {
     "init_hook": "export HOOK=hook",

testscripts/shellenv/node/devbox.json

@@ -1,6 +1,6 @@
 {
   "packages": [
-    "nodejs-18_x"
+    "nodejs@18"
   ],
   "shell": {
     "init_hook": [
@@ -13,4 +13,4 @@
   "nixpkgs": {
     "commit": "4a65e9f64e53fdca6eed31adba836717a11247d2"
   }
-}
+}