BUG: make pct_change can handle the anchored freq #28664
- [x] closes #28664
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

    pct_change didn't work when the freq is anchored(like `1W`, `1M`, `BM`)
    so when the freq is anchored, use `data.asfreq(freq)` instead of the raw
    `data`.