cargo: bump syn from 2.0.13 to 2.0.15

Bumps [syn](https://github.com/dtolnay/syn) from 2.0.13 to 2.0.15.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](https://github.com/dtolnay/syn/compare/2.0.13...2.0.15)

---
updated-dependencies:
- dependency-name: syn
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Cargo.lock

@@ -270,7 +270,7 @@ checksum = "b9ccdd8f2a161be9bd5c023df56f1b2a0bd1d83872ae53b71a84a12c9bf6e842"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.13",
+ "syn 2.0.15",
 ]
 
 [[package]]
@@ -1277,7 +1277,7 @@ name = "deltachat_derive"
 version = "2.0.0"
 dependencies = [
  "quote",
- "syn 2.0.13",
+ "syn 2.0.15",
 ]
 
 [[package]]
@@ -2057,7 +2057,7 @@ checksum = "89ca545a94061b6365f2c7355b4b32bd20df3ff95f02da9329b34ccc3bd6ee72"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.13",
+ "syn 2.0.15",
 ]
 
 [[package]]
@@ -4313,7 +4313,7 @@ checksum = "4c614d17805b093df4b147b51339e7e44bf05ef59fba1e45d83500bcfb4d8585"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.13",
+ "syn 2.0.15",
 ]
 
 [[package]]
@@ -4620,9 +4620,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.13"
+version = "2.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4c9da457c5285ac1f936ebd076af6dac17a61cfe7826f2076b4d015cf47bc8ec"
+checksum = "a34fcf3e8b60f57e6a14301a2e916d323af98b0ea63c599441eec8558660c822"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -4752,7 +4752,7 @@ checksum = "f9456a42c5b0d803c8cd86e73dd7cc9edd429499f37a3550d286d5e86720569f"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.13",
+ "syn 2.0.15",
 ]
 
 [[package]]
@@ -4865,7 +4865,7 @@ checksum = "61a573bdc87985e9d6ddeed1b3d864e8a302c847e40d647746df2f1de209d1ce"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.13",
+ "syn 2.0.15",
 ]
 
 [[package]]