CI: Use year and week number cache key for -master and -latest

[junaruga]

This PR is a follow-up for #1109 (790ed93). This PR includes the current year and week number by date -u '+%Y%W' in the cache key for openssl-master, libressl-master, and aws-lc-latest to ensure the cached builds are refreshed weekly.

$ date -u '+%Y%W'
202636

I tested the openssl-master and aws-lc-latest cases in my fork repository. The log is below.

https://github.com/junaruga/ruby-openssl/actions/runs/34144869607/job/101814592780#step:4:4

Run actions/cache@v6
  with:
    path: ~/openssl
    key: openssl-Linux-openssl-master-default-202636
    enableCrossOsArchive: false
    fail-on-cache-miss: false
    lookup-only: false
    save-always: false
Cache not found for input keys: openssl-Linux-openssl-master-default-202636

https://github.com/junaruga/ruby-openssl/actions/runs/34144869607/job/101814592774#step:4:4

Run actions/cache@v6
  with:
    path: ~/openssl
    key: openssl-Linux-aws-lc-latest-default-202636
    enableCrossOsArchive: false
    fail-on-cache-miss: false
    lookup-only: false
    save-always: false
Cache not found for input keys: openssl-Linux-aws-lc-latest-default-202636

Commit message

The commit 790ed93 ("CI: enable caching for
openssl-master, libressl-master, and aws-lc-latest") assumed that caches expire
after a week, but they only expire if not accessed within that period. On an
active repository, the cache would be accessed on every CI run and remain
permanently stale.

https://github.com/actions/cache#cache-limits

Include the current year and week number in the cache key for openssl-master,
libressl-master, and aws-lc-latest to ensure the cached builds are refreshed
weekly.

http://man7.org/linux/man-pages/man1/date.1.html

   %W     week number of year, with Monday as first day of week
          (00..53)

Assisted-by: Claude:Opus 4.6

[rhenium]

Thanks! This looks even better.