spack.yaml: acts@15.1.0

spack.yaml

 spack:
   specs:
-    - acts@14.1.0 +dd4hep +digitization +identification +json +tgeo +ipo +examples +fatras +geant4
+    - acts@15.1.0 +dd4hep +digitization +identification +json +tgeo +ipo +examples +fatras +geant4
     - cairo@1.16.0 +fc+ft+X+pdf+gobject
     - clhep@2.4.4.0 cxxstd=17
     - cmake@3.21.4