all: fix spelling mistakes

Signed-off-by: Josh Soref <2119212+jsoref@users.noreply.github.com>

tstest/clock.go

@@ -25,7 +25,7 @@ type Clock struct {
 	sync.Mutex
 }
 
-// Now returns the virtual clock's current time, and avances it
+// Now returns the virtual clock's current time, and advances it
 // according to its step configuration.
 func (c *Clock) Now() time.Time {
 	c.Lock()