Add lower bounds for transitive deps

[jmid]

opam's lower bounds check is effective to the point that it finds an annoying combination involving

• ocaml-compiler-libs.v0.11.0
• ppx_derivers.1.0
• biniou.1.2.0

which are all transitive dependencies of mutaml that make the cram diff tests fail because of warnings such as the following:

+  File "/home/opam/.opam/4.12/lib/ocaml-compiler-libs/toplevel/ocaml-compiler-libs.toplevel.dune", line 1, characters 0-0:
+  Warning: .dune files are ignored since 2.0. Reinstall the library with dune
+  >= 2.0 to get rid of this warning and enable support for the subsystem this
+  library provides.
+  File "/home/opam/.opam/4.12/lib/ppx_derivers/ppx_derivers.dune", line 1, characters 0-0:
+  Warning: .dune files are ignored since 2.0. Reinstall the library with dune
+  >= 2.0 to get rid of this warning and enable support for the subsystem this
+  library provides.
+  File "/home/opam/.opam/4.12/lib/biniou/biniou.dune", line 1, characters 0-0:
+  Warning: .dune files are ignored since 2.0. Reinstall the library with dune
+  >= 2.0 to get rid of this warning and enable support for the subsystem this
+  library provides.

Rather than filter output further, this PR adds suitable lower bounds for transitive deps. Incrementing yojson to min. 2.0.0 avoids a transitive biniou dependency.

With this PR only two red CI lights remain:

• an internal parse error in the experimental opam-dune-lint.dev
• 4.14 ppc64 errors because some mutations cause timeouts rather than errors (due to slowness or missing overflow protection I suspect)