apk should prune obsolete indices
On my machine:
treefort:~$ ls -al /var/cache/apk/APKINDEX.*
-rw-r--r-- 1 root root 656814 Sep 22 2020 /var/cache/apk/APKINDEX.066df28d.tar.gz
-rw-r--r-- 1 root root 634253 Sep 6 2020 /var/cache/apk/APKINDEX.2c4ac24e.tar.gz
-rw-r--r-- 1 root root 633808 Sep 22 2020 /var/cache/apk/APKINDEX.30e6f5af.tar.gz
-rw-r--r-- 1 root root 1145983 Sep 6 2020 /var/cache/apk/APKINDEX.40a3604f.tar.gz
-rw-r--r-- 1 root root 1566651 Jun 25 13:03 /var/cache/apk/APKINDEX.74fbe57d.tar.gz
-rw-r--r-- 1 root root 642689 Jun 25 13:03 /var/cache/apk/APKINDEX.924f3f67.tar.gz
-rw-r--r-- 1 root root 1226681 Sep 22 2020 /var/cache/apk/APKINDEX.b53994b4.tar.gz
-rw-r--r-- 1 root root 638355 Jun 25 13:03 /var/cache/apk/APKINDEX.e3b89664.tar.gz
@mps has also noticed similar. We should garbage collect these obsolete indices.