chore: point requirements to modified branches

Author: alexfikl

requirements.txt

@@ -12,5 +12,5 @@ git+https://github.com/inducer/boxtree.git#egg=boxtree
 git+https://github.com/inducer/arraycontext.git#egg=arraycontext
 git+https://github.com/inducer/gmsh_interop/#egg=gmsh_interop
 git+https://github.com/inducer/meshmode.git#egg=meshmode
-git+https://github.com/inducer/sumpy.git#egg=sumpy
+git+https://github.com/inducer/sumpy.git@towards-array-context-merge#egg=sumpy
 git+https://github.com/inducer/pyfmmlib.git#egg=pyfmmlib