doc: fix various typos

Found via `codespell -q 3 -L atleast,iinclude,ist,programm,reenable,ser,uptodate`

internal/restorer/filerestorer.go

@@ -359,7 +359,7 @@ func (r *fileRestorer) downloadBlobs(ctx context.Context, packID restic.ID,
 			}
 			for file, offsets := range blob.files {
 				for _, offset := range offsets {
-					// avoid long cancelation delays for frequently used blobs
+					// avoid long cancellation delays for frequently used blobs
 					if ctx.Err() != nil {
 						return ctx.Err()
 					}