Try actually writing the stdin to stdout in powershell

tests/process/exec/stdin.luau

@@ -2,12 +2,13 @@ local process = require("@lune/process")
 
 local expected = "Hello from child process!"
 
--- NOTE: This requires "bash" to be installed even for Windows
--- users, testing a simple cat from stdin to stdout using pwsh
--- has unfortunately proved to be a significant challenge...
 local options = { stdio = { stdin = expected } }
 local result = if process.os == "windows"
-	then process.exec("powershell", { "-Command", "[System.Console]::In.ReadToEnd()" }, options)
+	then process.exec(
+		"powershell",
+		{ "-Command", "[System.Console]::Write([System.Console]::In.ReadToEnd())" },
+		options
+	)
 	else process.exec("bash", { "-c", "cat" }, options)
 
 local resultStdout = result.stdout
@@ -15,5 +16,7 @@ resultStdout = string.gsub(resultStdout, "^%s+", "") -- Trim leading whitespace
 resultStdout = string.gsub(resultStdout, "%s+$", "") -- Trim trailing whitespace
 assert(
 	resultStdout == expected,
-	"Stdin passing did not return proper output!" .. `\nExpected: {expected}` .. `\nReceived: {resultStdout}`
+	"Passing a string to stdin did not return the expected output!"
+		.. `\nExpected: {expected}`
+		.. `\nReceived: {resultStdout}`
 )