Bump modem7/borgmatic-docker from 1.5.20 to 1.5.21 in /base-dockercli

Bumps modem7/borgmatic-docker from 1.5.20 to 1.5.21.

---
updated-dependencies:
- dependency-name: modem7/borgmatic-docker
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

base-dockercli/Dockerfile

@@ -1,4 +1,4 @@
-FROM modem7/borgmatic-docker:1.5.20
+FROM modem7/borgmatic-docker:1.5.21
 COPY entry.sh /entry.sh
 RUN apk update \
     && apk add --no-cache \