workflows: Trigger docker-petsc wf

Author: ZoeLeibowitz

.github/workflows/docker-petsc.yml

@@ -7,6 +7,10 @@ on:
   push:
     branches:
       - petsc         # Push events on petsc branch
+  # TODO: drop this
+  pull_request:
+    branches:
+      - petsc
 
 jobs:
   build-and-push:

devito/petsc/solver_parameters.py

@@ -1,7 +1,11 @@
 import itertools
 
-from petsctools import flatten_parameters
-
+try:
+    from petsctools import flatten_parameters
+except ImportError:
+    # TODO: drop
+    def flatten_parameters():
+        raise ImportError("petsctools is not installed")
 
 # NOTE: Will be extended, the default preconditioner is not going to be 'none'
 base_solve_defaults = {