Overnight-tests: mesa-aco/mesa.bst fails fetch

https://gitlab.com/BuildStream/buildstream/-/jobs/350062918 and https://gitlab.com/BuildStream/buildstream/-/jobs/350062949

looks like fetching fails

FAILURE git source at extensions/mesa-aco/mesa.bst [line 150 column 2]: expected ref '6c3bad5214b230ccfc99a459ee46f2130b19eede' was not found in git repository: 'github:daniel-schuermann/mesa.git'