client: use os/exec/Cmd.Environ() instead of os.Environ()

Don't set Env if not set; the default is already handled if it's nil; from
the documentation: https://pkg.go.dev/os/exec@go1.20.4#Cmd.Env

    // If Env is nil, the new process uses the current process's
    // environment.

Use `os/exec/Cmd.Environ()` instead of `os.Environ()`, which was added in
go1.19, and handles additional environment variables, such as `PWD` on POSIX
systems, and `SYSTEMROOT` on Windows. https://pkg.go.dev/os/exec@go1.20.4#Cmd.Environ

Also remove a redundant `fmt.Sprintf()`, as we're only concatenating strings.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client/command.go

@@ -1,7 +1,6 @@
 package client
 
 import (
-	"fmt"
 	"io"
 	"os"
 	"os/exec"
@@ -30,10 +29,9 @@ func NewShellProgramFuncWithEnv(name string, env *map[string]string) ProgramFunc
 
 func createProgramCmdRedirectErr(commandName string, args []string, env *map[string]string) *exec.Cmd {
 	programCmd := exec.Command(commandName, args...)
-	programCmd.Env = os.Environ()
 	if env != nil {
 		for k, v := range *env {
-			programCmd.Env = append(programCmd.Env, fmt.Sprintf("%s=%s", k, v))
+			programCmd.Env = append(programCmd.Environ(), k+"="+v)
 		}
 	}
 	programCmd.Stderr = os.Stderr