upgrade alpine base image to v3.15.0 including upgrade of borgbackup package to v1.1.17-r1 & openssh-server package to v8.8_p1-r1 (see below)

https://github.com/borgbackup/borg/blob/1.1.17/docs/changes.rst#version-1117-2021-07-12
https://git.alpinelinux.org/aports/commit/community/borgbackup?h=3.15-stable&id=35d5217f8ab943f05ff14545ed8a97867e1cb00d
https://git.alpinelinux.org/aports/commit/community/borgbackup?h=3.15-stable&id=33d78f165de327f378f4fbc1fa671d1dbeb50ef8
https://git.alpinelinux.org/aports/commit/community/borgbackup?h=3.15-stable&id=75cbcc242479a37dc803ef29629682ac9d445ff9

https://web.archive.org/web/20211204063543/https://www.openssh.com/releasenotes.html
https://git.alpinelinux.org/aports/commit/main/openssh?h=3.15-stable&id=8293eb79d181515827092ec15f9dcb24989959c6
https://git.alpinelinux.org/aports/commit/main/openssh?h=3.15-stable&id=e05faf293fd802c729d432906ffb5e8db77f3830
https://git.alpinelinux.org/aports/commit/main/openssh?h=3.15-stable&id=b5e3d52e5a95ff8a73c23908201474bb15048a11

https://github.com/fphammerle/docker-borgbackup-client/commit/04610b728c8ec3c83f7618b1641aabb97b3346af
https://github.com/fphammerle/docker-sftpd/commit/fc472ac4fbc12a25e8831cab197711104923b775

Dockerfile

@@ -1,7 +1,7 @@
-FROM docker.io/alpine:3.14.3
+FROM docker.io/alpine:3.15.0
 
-ARG BORGBACKUP_PACKAGE_VERSION=1.1.16-r1
-ARG OPENSSH_SERVER_PACKAGE_VERSION=8.6_p1-r3
+ARG BORGBACKUP_PACKAGE_VERSION=1.1.17-r1
+ARG OPENSSH_SERVER_PACKAGE_VERSION=8.8_p1-r1
 ARG TINI_PACKAGE_VERSION=0.19.0-r0
 ARG USER=borg
 ENV SSHD_HOST_KEYS_DIR=/etc/ssh/host_keys

borgbackup-package-log.url

@@ -0,0 +1 @@
+https://git.alpinelinux.org/aports/log/community/borgbackup?h=3.15-stable

openssh-package-log.url

@@ -1 +1 @@
-https://git.alpinelinux.org/aports/log/main/openssh
+https://git.alpinelinux.org/aports/log/main/openssh?h=3.15-stable