rstanarm v2.26.1

This release updates rstanarm to use the latest syntax supported by rstan.

What's Changed

• wells dataset wrong variable name by @storopoli in #552
• add logo to be displayed in r-universe by @avehtari in #569
• Fix CRAN NOTEs and failures by @andrjohns in #587
• Implement posterior::as_draws() for rstanarm objects by @jgabry in #596
• Array syntax by @bgoodri in #597

Full Changelog: v2.21.3...v2.26.1