spec_exec: don't use wildcard '_' in QueryError match

Since last time, during error refactor I introduced a silent
bug to the code (#1075),
I'd like to prevent that from happening in the future. This is why
we replace a `_` match with explicit error variants when deciding
if error received from speculative execution should be ignored.

scylla/src/transport/speculative_execution.rs

@@ -85,10 +85,23 @@ impl SpeculativeExecutionPolicy for PercentileSpeculativeExecutionPolicy {
 fn can_be_ignored<ResT>(result: &Result<ResT, QueryError>) -> bool {
     match result {
         Ok(_) => false,
-        Err(QueryError::BrokenConnection(_)) => true,
-        Err(QueryError::ConnectionPoolError(_)) => true,
-        Err(QueryError::TimeoutError) => true,
-        _ => false,
+        Err(e) => match e {
+            QueryError::BrokenConnection(_)
+            | QueryError::ConnectionPoolError(_)
+            | QueryError::TimeoutError => true,
+
+            QueryError::DbError(_, _)
+            | QueryError::BadQuery(_)
+            | QueryError::CqlRequestSerialization(_)
+            | QueryError::BodyExtensionsParseError(_)
+            | QueryError::EmptyPlan
+            | QueryError::CqlResultParseError(_)
+            | QueryError::CqlErrorParseError(_)
+            | QueryError::MetadataError(_)
+            | QueryError::ProtocolError(_)
+            | QueryError::UnableToAllocStreamId
+            | QueryError::RequestTimeout(_) => false,
+        },
     }
 }