fix(provider-tck): check the control response body's Close

`defer resp.Body.Close()` discards an error errcheck requires to be handled,
so `make lint` failed on the suite module and, by inheritance, on all three
stacked branches.

The shape was invisible until this client moved onto the base branch: at its
previous home in providers/flagd/e2e it sat behind `//go:build e2e`, and
golangci-lint does not analyse files excluded by a build tag. Nothing about the
code changed -- only whether anything looked at it.

Discarded explicitly rather than logged: the request has already returned its
status, the body is drained immediately above, and a failure to close a body
the caller is finished with tells an adopter nothing it can act on. `_ =`
matches the `_, _ = io.Copy` on the following line.

Signed-off-by: Simon Schrottner <simon.schrottner@flagsmith.com>

Author: aepfli

tools/provider-tck/pkg/tck/httpcontrol.go

@@ -235,7 +235,7 @@ func (c *HTTPControl) call(ctx context.Context, path string, query url.Values) (
 			"reachable even while the backend is deliberately down, otherwise an outage cannot be ended",
 			target, err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	_, _ = io.Copy(io.Discard, resp.Body)