queryrange: retry: do not retry if context is canceled

My Thanos instance is spamming this whenever the user cancels a query
that is being executed:

```
{"caller":"retry.go:73","err":"context canceled","level":"error","msg":"error processing request","org_id":"anonymous","try":0,"ts":"2021-11-23T13:35:09.275914072Z"}
```

It doesn't mean anything bad so let's stop the spam. Thus, do not perform the
retrying logic if the context has been canceled. Later on this is handled in:

```go
	resp, err := f.roundTripper.RoundTrip(r)
	queryResponseTime := time.Since(startTime)

	if err != nil {
		writeError(w, err)
		return
	}
```

Signed-off-by: Giedrius Statkevičius <[email protected]>

Author: GiedriusS

pkg/querier/queryrange/retry.go

@@ -2,6 +2,7 @@ package queryrange
 
 import (
 	"context"
+	"errors"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -66,6 +67,10 @@ func (r retry) Do(ctx context.Context, req Request) (Response, error) {
 			return resp, nil
 		}
 
+		if errors.Is(err, context.Canceled) {
+			return nil, err
+		}
+
 		// Retry if we get a HTTP 500 or a non-HTTP error.
 		httpResp, ok := httpgrpc.HTTPResponseFromError(err)
 		if !ok || httpResp.Code/100 == 5 {