🐛 Possible race condition in delta testsuite with environment variable setting

[joshtriplett]

This failure occasionally occurs when running the delta testsuite:

---- env::tests::test_env_parsing_with_pager_set_to_bat stdout ----
thread 'env::tests::test_env_parsing_with_pager_set_to_bat' panicked at src/env.rs:79:9:
assertion `left == right` failed: Expected env.pagers.1 == Some(bat) but was Some("less")
  left: Some("less")
 right: Some("bat")
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This might be a race condition between tests (which run in parallel).