Log Message:
(math/R-forecast) Updated 8.21 to 8.23.0

# forecast 8.23.0
  * Prevented RNG state changing when the package is attached (#954, #955).
  * head.ts and tail.ts only defined for R < 4.5.0 due to new base R functions.

# forecast 8.22.0
  * hfitted now much faster for ARIMA models (danigiro, #949)
  * hfitted now much faster for ETS models, and produces fitted values from
    initial states (#950)

# forecast 8.21.1
  * nnetar now allows p or P to be 0
  * Bug fixes and improved docs