Tell CI to use for_rmg branch of RMS

Temorparily we will maintain a branch of ReactionMechanismSimulator.jl
that is specifically for use with RMG.
Thus `for_rmg` is a good name for it.
We used it once before, in August 2023.

This one is/was also called the marcus_development branch.
It includes all the commits necessary to make electrochemistry work
but doesn't include changes for the RMG-RMS interface overhaul.

This commit will be reverted when for_rmg gets merged into RMS main.

.github/workflows/CI.yml

@@ -98,7 +98,7 @@ jobs:
         timeout-minutes: 120 # this usually takes 20-45 minutes (or hangs for 6+ hours).
         run: |
           python -c "import julia; julia.install(); import diffeqpy; diffeqpy.install()"
-          julia -e 'using Pkg; Pkg.add(PackageSpec(name="ReactionMechanismSimulator",rev="main")); using ReactionMechanismSimulator'
+          julia -e 'using Pkg; Pkg.add(PackageSpec(name="ReactionMechanismSimulator",rev="for_rmg")); using ReactionMechanismSimulator'
 
       - name: Install Q2DTor
         run: echo "" | make q2dtor