Merge pull request #728 from LinqLover/linux64x64/squeak.sista.spur

[ci] add squeak.sista.spur build for linux64x64

Author: marceltaeumel

.github/workflows/linux.yml

@@ -62,7 +62,10 @@ jobs:
           - debug
           - assert
         include:
-          # sista build not fully prepared for linux64x64, so only choose selected configurations for linux32x86
+          - arch: linux64x64
+            flavor: squeak.sista.spur
+            heartbeat: threaded
+            mode: fast
           - arch: linux32x86
             flavor: squeak.sista.spur
             heartbeat: threaded