Bump golang in /custom-metrics-stackdriver-adapter

Bumps golang from 1.21-alpine to 1.22-alpine.

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

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

custom-metrics-stackdriver-adapter/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM golang:1.21-alpine as builder
+FROM golang:1.22-alpine as builder
 WORKDIR ${GOPATH}/src/github.com/GoogleCloudPlatform/k8s-stackdriver/custom-metrics-stackdriver-adapter
 COPY . ./
 RUN CGO_ENABLED=0 GOOS=linux go build -mod=readonly -o /adapter