message: fix typo in metric description
diff: @@ -43,7 +43,7 @@ macro_rules! metrics {
  cdn_invalidation_time: prometheus::HistogramVec::new(
  prometheus::HistogramOpts::new(
  "cdn_invalidation_time",
  - "duration of CDN invalidations after having beeing sent to the CDN.",
  + "duration of CDN invalidations after having been sent to the CDN.",
  )
  .buckets($crate::metrics::CDN_INVALIDATION_HISTOGRAM_BUCKETS.to_vec())
  .variable_label("distribution"),
  