chore(deps): update alpine docker tag to v3.21.0 (#6315)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| alpine | final | minor | `3.20.3` -> `3.21.0` |
| alpine | stage | minor | `3.20.3` -> `3.21.0` |

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Signed-off-by: Mend Renovate <[email protected]>

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docker/base/Dockerfile

@@ -1,9 +1,9 @@
 # Copyright (c) 2024 The Jaeger Authors.
 # SPDX-License-Identifier: Apache-2.0
 
-FROM alpine:3.20.3 AS cert
+FROM alpine:3.21.0 AS cert
 RUN apk add --update --no-cache ca-certificates mailcap
 
-FROM alpine:3.20.3
+FROM alpine:3.21.0
 COPY --from=cert /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
 COPY --from=cert /etc/mime.types /etc/mime.types