Fix missing c/chr in preparation of cli message

[brookslogan]

{cli_,}{abort,warn,inform} expect the entire message inside message; ... is used to add named fields to the condition object that they create (so you can extract extra info from, e.g., rlang::last_error()$<name>). I'm getting

Error in `warning_cnd()`:
! Conditions must have named data fields
---
Backtrace:
    ▆
 1. ├─epidatr::pub_covidcast(...)
 2. │ └─... %>% fetch(fetch_args = fetch_args) at cmu-delphi-epidatr-b5f819a/R/endpoints.R:747:2
 3. ├─epidatr::fetch(., fetch_args = fetch_args)
 4. │ └─epidatr:::cache_epidata_call(epidata_call, fetch_args = fetch_args) at cmu-delphi-epidatr-b5f819a/R/epidatacall.R:207:2
 5. │   └─cli::cli_warn(...) at cmu-delphi-epidatr-b5f819a/R/cache.R:253:6
 6. │     └─rlang::warn(format_warning(message, .envir = .envir), ...)
 7. │       └─rlang::warning_cnd(...)
 8. └─rlang::abort(message = message)

from

      cli::cli_warn("using cached results with `as_of` within the past week (or the future!). This will likely result ",
        "in an invalid cache. Consider\n",
        "1. disabling the cache for this session with `disable_cache` or permanently with environmental ",
        "variable `EPIDATR_USE_CACHE=FALSE`\n",
        "2. setting `EPIDATR_CACHE_MAX_AGE_DAYS={Sys.getenv('EPIDATR_CACHE_MAX_AGE_DAYS', unset = 1)}` to e.g. `3/24` ",
        "(3 hours).",
        .frequency = "regularly",
        .frequency_id = "cache timing issues",
        class = "cache_recent_data"
      )

Fix is just wrapping up all the message parts in a character vector using c.

[dshemetov]

Right, this should do it

cli::cli_warn(
  c(
    "Using cached results with `as_of` within the past week (or the future!).
    This will likely result in an invalid cache. Consider:",
    "i" = "disabling the cache for this session with `disable_cache` or
           permanently with environmental variable `EPIDATR_USE_CACHE=FALSE`",
    "i" = "setting
          `EPIDATR_CACHE_MAX_AGE_DAYS={Sys.getenv('EPIDATR_CACHE_MAX_AGE_DAYS',
          unset = 1)}` to e.g. `3/24` (3 hours)."
  ),
  .frequency = "regularly",
  .frequency_id = "cache timing issues",
  class = "cache_recent_data"
)