cargo: bump once_cell from 1.13.1 to 1.15.0

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.13.1 to 1.15.0.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](https://github.com/matklad/once_cell/compare/v1.13.1...v1.15.0)

---
updated-dependencies:
- dependency-name: once_cell
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.lock

@@ -2286,9 +2286,9 @@ dependencies = [
 
 [[package]]
 name = "once_cell"
-version = "1.13.1"
+version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "074864da206b4973b84eb91683020dbefd6a8c3f0f38e054d93954e891935e4e"
+checksum = "e82dad04139b71a90c080c8463fe0dc7902db5192d939bd0950f074d014339e1"
 
 [[package]]
 name = "oorandom"

Cargo.toml

@@ -46,7 +46,7 @@ native-tls = "0.2"
 num_cpus = "1.13"
 num-derive = "0.3"
 num-traits = "0.2"
-once_cell = "1.13.1"
+once_cell = "1.15.0"
 percent-encoding = "2.0"
 pgp = { version = "0.8", default-features = false }
 pretty_env_logger = { version = "0.4", optional = true }

deltachat-ffi/Cargo.toml

@@ -25,7 +25,7 @@ tokio = { version = "1", features = ["rt-multi-thread"] }
 anyhow = "1"
 thiserror = "1"
 rand = "0.7"
-once_cell = "1.13.1"
+once_cell = "1.15.0"
 
 [features]
 default = ["vendored"]