`tz"Z"` should be `==` to `tz"UTC"`

[kleinschmidt]

These are AFAICT identical (besides the name) but are not ==:

julia> tz"Z" |> dump
FixedTimeZone
  name: InlineStrings.String15 InlineStrings.String15("Z")
  offset: TimeZones.UTCOffset
    std: Dates.Second
      value: Int64 0
    dst: Dates.Second
      value: Int64 0

julia> tz"UTC" |> dump
FixedTimeZone
  name: InlineStrings.String15 InlineStrings.String15("UTC")
  offset: TimeZones.UTCOffset
    std: Dates.Second
      value: Int64 0
    dst: Dates.Second
      value: Int64 0

julia> tz"Z" == tz"UTC"
false