v1.21.2

Plots v1.21.2

Diff since v1.21.1

Closed issues:

• [BUG] LaTeXString in ticks errors for pgfplotsx (#3375)
• [BUG] PGFPlotsX backend handles some preamble options incorrectly (#3771)

Merged pull requests:

• improve axis decorations (#3756) (@BeastyBlacksmith)
• sanitize axis strings in pgfplotsx (#3772) (@BeastyBlacksmith)
• UnicodePlots: heatmap support (#3774) (@t-bltg)
• Move codecov.yml (#3777) (@t-bltg)
• merge root codecov.yml (#3779) (@t-bltg)