Bump alpine from 3.20 to 3.21 (#73)

Bumps alpine from 3.20 to 3.21.

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

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

Dockerfile

@@ -17,7 +17,7 @@ COPY . .
 RUN go build -o vulcan-stream -a -tags netgo -ldflags '-w' cmd/vulcan-stream/main.go
 
 # final stage
-FROM alpine:3.20
+FROM alpine:3.21
 RUN apk add --no-cache --update gettext
 
 ARG BUILD_RFC3339="1970-01-01T00:00:00Z"