Stop leaking path

[alfa07]

Leak creates noise and prevents from running sanitizer in CI

Address sanitizer complains about memory leak here: https://github.com/mitsuhiko/insta/blob/master/src/runtime.rs#L204
Like this:

$ RUST_BACKTRACE=1 RUSTFLAGS=-Zsanitizer=address cargo test --target x86_64-unknown-linux-gnu
..... skipped ....
=================================================================
==2927823==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 24 byte(s) in 1 object(s) allocated from:
    #0 0x5593809c790d in malloc /rustc/llvm/src/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x5593810d7f48 in alloc::alloc::alloc::h8d7eb83558c3a58a /home/maxim/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:86:14
    #2 0x5593810d7f48 in alloc::alloc::Global::alloc_impl::h9eeeef21ad1fa569 /home/maxim/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:166:73
    #3 0x5593810d7f48 in _$LT$alloc..alloc..Global$u20$as$u20$core..alloc..Allocator$GT$::allocate::hff4002a2175a8570 /home/maxim/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:226:9
    #4 0x5593810d7f48 in alloc::alloc::exchange_malloc::hb01d0b8a035cc1a4 /home/maxim/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:316:11
    #5 0x5593810d7f48 in alloc::boxed::Box$LT$T$GT$::new::h0aec4b78846d8d44 /home/maxim/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/boxed.rs:185:9
    #6 0x5593810d7f48 in insta::runtime::get_cargo_workspace::hd14cebdfc963ae90 /home/maxim/.cargo/registry/src/github.com-1ecc6299db9ec823/insta-1.7.1/src/runtime.rs:204:30
    #7 0x5593810ea877 in insta::runtime::assert_snapshot::h4bbd9fa593b577e7 /home/maxim/.cargo/registry/src/github.com-1ecc6299db9ec823/insta-1.7.1/src/runtime.rs:888:27
    #8 0x559380bcf262 in alicedb::core::rowset::test::test_intersect::h39191c2839e78e11 /home/maxim/dev/alicedb/src/core/rowset.rs:347:9
    #9 0x559380e740d5 in core::ops::function::FnOnce::call_once::hc6d33e7538d37f7d /rustc/45b3c28518e4c45dfd12bc2c4400c0d0e9639927/library/core/src/ops/function.rs:227:5
    #10 0x559380e740d5 in test::__rust_begin_short_backtrace::h38a84db7bd777a3b /rustc/45b3c28518e4c45dfd12bc2c4400c0d0e9639927/library/test/src/lib.rs:567:5

SUMMARY: AddressSanitizer: 24 byte(s) leaked in 1 allocation(s).
error: test failed, to rerun pass '--lib'

Reproduction steps

1. Run RUST_BACKTRACE=1 RUSTFLAGS=-Zsanitizer=address cargo test --target x86_64-unknown-linux-gnu

Additional helpful information:

• Version of insta: 1.7.1
• Version of rustc: rustc 1.52.0-nightly (45b3c2851 2021-03-04)
• Operating system and version: Ubuntu 20.04.2 LTS

What did you expect

No errors from sanitizer