This pull requests introduces changes that make the use of the `test_context` macro more flexible.
Now, if the teardown is not skipped (default behavior), either an `immutable` or a `mutable` reference can be used for the context.
If the teardown is skipped with the `skip_teardown` option, an `immutable`, a `mutable` reference or full ownership can be taken.
So now the following is possible:
```rust
#[test_context(TeardownPanicContext, skip_teardown)]
#[tokio::test]
async fn test_async_skip_teardown(_ctx: &mut TeardownPanicContext) {}
#[test_context(TeardownPanicContext, skip_teardown)]
#[tokio::test]
async fn test_async_skip_teardown_with_immutable_ref(_ctx: &TeardownPanicContext) {}
#[test_context(TeardownPanicContext, skip_teardown)]
#[tokio::test]
async fn test_async_skip_teardown_with_full_ownership(_ctx: TeardownPanicContext) {}
#[test_context(TeardownPanicContext, skip_teardown)]
#[test]
fn test_sync_skip_teardown(_ctx: &mut TeardownPanicContext) {}
#[test_context(TeardownPanicContext, skip_teardown)]
#[test]
fn test_sync_skip_teardown_with_immutable_ref(_ctx: &TeardownPanicContext) {}
#[test_context(TeardownPanicContext, skip_teardown)]
#[test]
fn test_sync_skip_teardown_with_full_ownership(_ctx: TeardownPanicContext) {}
```
