v0.95.19

Oceananigans v0.95.19

Diff since v0.95.18

Merged pull requests:

• Add support for ZStar in RK3 (#4156) (@simone-silvestri)
• Remove if-statement from tridiagonal solver sweep (#4170) (@glwagner)
• Bump to 0.95.20 (#4171) (@glwagner)