Bump bdk from `919522a` to `8c21bcf`

Bumps [bdk](https://github.com/bitcoindevkit/bdk) from `919522a` to `8c21bcf`.
- [Release notes](https://github.com/bitcoindevkit/bdk/releases)
- [Commits](919522a456...8c21bcf40a1fe76637b65c3e483b6c46351f28fa)

---
updated-dependencies:
- dependency-name: bdk
  dependency-type: direct:production
...

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

Cargo.lock

@@ -146,7 +146,7 @@ dependencies = [
 [[package]]
 name = "bdk"
 version = "0.11.1-dev"
-source = "git+https://github.com/bitcoindevkit/bdk/#919522a456f40ffed8bb084d4f11a34e74197b10"
+source = "git+https://github.com/bitcoindevkit/bdk/#8c21bcf40a1fe76637b65c3e483b6c46351f28fa"
 dependencies = [
  "async-trait",
  "bdk-macros",
@@ -165,7 +165,7 @@ dependencies = [
 [[package]]
 name = "bdk-macros"
 version = "0.5.0"
-source = "git+https://github.com/bitcoindevkit/bdk/#919522a456f40ffed8bb084d4f11a34e74197b10"
+source = "git+https://github.com/bitcoindevkit/bdk/#8c21bcf40a1fe76637b65c3e483b6c46351f28fa"
 dependencies = [
  "proc-macro2",
  "quote",