Rename remaining jitterSeed -> offsetSeed variables (#12414)

I had changed the naming from "jitter" to "offset" in:

cb045c0e4b

...but I forgot to add this file to the commit to complete the renaming,
doing that now.

Signed-off-by: Julius Volz <julius.volz@gmail.com>

scrape/target.go

@@ -154,14 +154,14 @@ func (t *Target) hash() uint64 {
 }
 
 // offset returns the time until the next scrape cycle for the target.
-// It includes the global server jitterSeed for scrapes from multiple Prometheus to try to be at different times.
-func (t *Target) offset(interval time.Duration, jitterSeed uint64) time.Duration {
+// It includes the global server offsetSeed for scrapes from multiple Prometheus to try to be at different times.
+func (t *Target) offset(interval time.Duration, offsetSeed uint64) time.Duration {
 	now := time.Now().UnixNano()
 
 	// Base is a pinned to absolute time, no matter how often offset is called.
 	var (
 		base   = int64(interval) - now%int64(interval)
-		offset = (t.hash() ^ jitterSeed) % uint64(interval)
+		offset = (t.hash() ^ offsetSeed) % uint64(interval)
 		next   = base + int64(offset)
 	)