I hit a silly error while running unit tests under one version of python where that installed version was built against an older ncurses that didn't have a terminfo entry for ghostty, and the expected output wasn't correct because the output it actually got included a preamble about how it didn't know about xterm-ghostty. This change adds TERM=dumb to our standard environment used when running subprocesses. Like the existing language/ctype variables, this helps ensure that we have a consistent environment. Testing Done: Ran tests under the "broken" 3.14 install I had and saw that they now all passed.