Fix flickering test in CI

While this test always worked on my machine, it flickered in CI. And to
be fair the test can't guarantee the condition it is testing. Work
around this by trying many times before admitting failure.

internal/iobufpool/iobufpool_test.go

@@ -5,7 +5,6 @@ import (
 
 	"github.com/jackc/pgx/v5/internal/iobufpool"
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
 func TestGetCap(t *testing.T) {
@@ -70,9 +69,17 @@ func TestPutHandlesWrongSizedBuffers(t *testing.T) {
 }
 
 func TestPutGetBufferReuse(t *testing.T) {
-	buf := iobufpool.Get(4)
-	buf[0] = 1
-	iobufpool.Put(buf)
-	buf = iobufpool.Get(4)
-	require.Equal(t, byte(1), buf[0])
+	// There is no way to guarantee a buffer will be reused. It should be, but a GC between the Put and the Get will cause
+	// it not to be. So try many times.
+	for i := 0; i < 100000; i++ {
+		buf := iobufpool.Get(4)
+		buf[0] = 1
+		iobufpool.Put(buf)
+		buf = iobufpool.Get(4)
+		if buf[0] == 1 {
+			return
+		}
+	}
+
+	t.Error("buffer was never reused")
 }