Analysis tests cannot see TestEnvironment added environment variables in actions

Test rules can return `testing.TestEnvironment` to include custom environment variables for when the test is run. This works, however, they are not visible in the action object that an analysis test sees.

(incomplete) repro:

```
def foo_test_impl(ctx):
return [testing.TestEnvironment({"FOO": "BAR"})]

def verify_foo_test(ctx):
env = analysistest.begin(ctx)
actions = analysistest.target_actions(env)
for a in actions:
print(a.env)
return analysistest.end(env)
```

Expected: The "Testing ..." action should have FOO=BAR as one of its environment variable.

Actual: The FOO=BAR env var is not shown in the action's env values.

Start with the incomplete reproduction using testing.TestEnvironment and the analysistest.begin, analysistest.target_actions, and analysistest.end entry points. Check why the Testing action's a.env omits FOO=BAR, then verify that the action exposes the returned environment variable while the analysis test still completes successfully.

Written by the indexing model from the issue text.