tasks dependencies should permit env var modifications

[jdx]

similar to how args can be provided, e.g.:

[tasks.test]
run = "test.sh"
[tasks.test-all]
depends = [
  {task = "test", env = {PROP = "a"}},
  {task = "test", env = {PROP = "b"}},
]

alternate syntax:

[tasks.test]
run = "test.sh"
[tasks.test-all]
depends = ["PROP=a test", "PROP=b test"]

alternate involves parsing and I feel is less obvious so I think I like it less. Also weird it's {env} {task} when you would actually need {env} mise run {task} if it was actually bash (which it isn't)