The Czech Republic was supplying arms to Ukraine at the time, so it is perfectly possible that the GRU decided to blow up a Czech arms depot. And things like that can sometimes go wrong. But the duo responsible would not then have been sent to Britain to splash the Novichok.
Even officially, Novichok has only ever killed one person, and she was a bystander. If the GRU or anyone else had wanted the Skripals dead, then they would have used a gun. But the main point is this: whatever the else the GRU may be, it is not a travel agency for Laurel and Hardy.