build(deps): bump the go-httpbin group across 2 directories with 1 update (#543)

Bumps the go-httpbin group with 1 update in the /.ci directory: [mccutchen/go-httpbin](https://github.com/mccutchen/go-httpbin).
Bumps the go-httpbin group with 1 update in the /.devcontainer directory: [mccutchen/go-httpbin](https://github.com/mccutchen/go-httpbin).


Updates `mccutchen/go-httpbin` from 2.20 to 2.21
- [Release notes](https://github.com/mccutchen/go-httpbin/releases)
- [Commits](mccutchen/go-httpbin@v2.20.0...v2.21.0)

Updates `mccutchen/go-httpbin` from 2.20 to 2.21
- [Release notes](https://github.com/mccutchen/go-httpbin/releases)
- [Commits](mccutchen/go-httpbin@v2.20.0...v2.21.0)

---
updated-dependencies:
- dependency-name: mccutchen/go-httpbin
  dependency-version: '2.21'
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: go-httpbin
- dependency-name: mccutchen/go-httpbin
  dependency-version: '2.21'
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: go-httpbin
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.ci/docker-compose.yml

@@ -16,7 +16,7 @@ services:
 
   httpbin:
     container_name: ci_httpbin
-    image: ghcr.io/mccutchen/go-httpbin:2.20
+    image: ghcr.io/mccutchen/go-httpbin:2.21
     ports:
       - "127.0.0.1:8081:8081"
     command: ["go-httpbin", "-port", "8081"]

.devcontainer/docker-compose.yml

@@ -26,7 +26,7 @@ services:
 
   httpbin:
     container_name: gotify-httpbin
-    image: ghcr.io/mccutchen/go-httpbin:2.20
+    image: ghcr.io/mccutchen/go-httpbin:2.21
     ports:
       - "8081:8081"
     command: ["go-httpbin", "-port", "8081"]