Merge branch 'dt/tests-with-env-not-subshell'

* dt/tests-with-env-not-subshell:
tests: use "env" to run commands with temporary env-var settings

diff --cc t/t1300-repo-config.sh
Simple merge

diff --cc t/t3200-branch.sh
Simple merge

diff --cc t/t3301-notes.sh
Simple merge

diff --cc t/t5801-remote-helpers.sh
Simple merge