Update to the new backtrace API #304

Update to the new backtrace API

Usage Workflow file

1 error and 14 warnings

embedded manifest `/home/runner/work/eyre/eyre/eyre/tests/ui/ui_test_backtrace.rs` requires `-Zscript`

The following actions uses node12 which is deprecated and will be forced to run on node16: actions-rs/toolchain@v1, actions-rs/cargo@v1. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L51

unused import: `std::backtrace::Backtrace`

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L13

function `low` is never used

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L22

function `med` is never used

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L30

function `high` is never used

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L41

static `BACKTRACE_SNIPPET_HIGH` is never used

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L60

function `test_backtrace_simple` is never used

Run actions-rs/cargo@v1: eyre/tests/test_backtrace.rs#L74

function `test_backtrace` is never used

`eyre` (test "test_backtrace") generated 7 warnings (run `cargo fix --test "test_backtrace"` to apply 1 suggestion)

the following packages contain code that will be rejected by a future version of Rust: nom v4.2.3