examples/capture.py: Pass HOME environment variable (primarily)

Symptom was:
> # python3 ./examples/capture.py output.txt asciinema rec -c 'timeout 3 htop' output.cast
> Traceback (most recent call last):
>   File "/usr/lib/python-exec/python3.10/asciinema", line 8, in <module>
>     sys.exit(main())
>   File "/usr/lib/python3.10/site-packages/asciinema/__main__.py", line 61, in main
>     cfg = config.load()
>   File "/usr/lib/python3.10/site-packages/asciinema/config.py", line 226, in load
>     config = Config(get_config_home(env), env)
>   File "/usr/lib/python3.10/site-packages/asciinema/config.py", line 216, in get_config_home
>     raise Exception(
> Exception: need $HOME or $XDG_CONFIG_HOME or $ASCIINEMA_CONFIG_HOME

examples/capture.py

@@ -24,8 +24,9 @@
 
     p_pid, master_fd = pty.fork()
     if p_pid == 0:  # Child.
-        os.execvpe(argv[0], argv,
-                   env=dict(TERM="linux", COLUMNS="80", LINES="24"))
+        env = os.environ.copy()
+        env.update(dict(TERM="linux", COLUMNS="80", LINES="24"))
+        os.execvpe(argv[0], argv, env=env)
 
     with open(output_path, "wb") as handle:
         while True: