Add missing Melange upper bounds

[jmid]

Spotted in #28866

There are a bunch of identical failures caused by mel.send.pipe having been deprecated and now removed:

#=== ERROR while compiling melange-fest.0.1.0 =================================#
# context              2.5.0~alpha1 | linux/x86_64 | ocaml-base-compiler.4.14.2 | file:///home/opam/opam-repository
# path                 ~/.opam/4.14/.opam-switch/build/melange-fest.0.1.0
# command              ~/.opam/opam-init/hooks/sandbox.sh build dune build -p melange-fest -j 71 @install
# exit-code            1
# env-file             ~/.opam/log/melange-fest-7-389dd8.env
# output-file          ~/.opam/log/melange-fest-7-389dd8.out
### output ###
# (cd _build/.sandbox/2320996745d06c91c6c2e0d6f35678e4/reason && .ppx/b36bc7dca4c367fe995383a780501242/ppx.exe --cookie 'library-name="fest"' -o src/fest.pp.ml --impl src/fest.ml -corrected-suffix .ppx-corrected -diff-cmd - -dump-ast)
# File "src/fest.ml", line 26, characters 0-28:
# 26 | [@@mel.send.pipe: assertion]
#      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: `mel.send.pipe' has been removed. Use `@mel.send' with the `@mel.this` marker instead.
# (cd _build/.sandbox/4cabdc118e6eb79b2fe5dde45e38905f/default && .ppx/b36bc7dca4c367fe995383a780501242/ppx.exe --cookie 'library-name="fest"' -o src/fest.pp.ml --impl src/fest.ml -corrected-suffix .ppx-corrected -diff-cmd - -dump-ast)
# File "src/fest.ml", line 26, characters 0-28:
# 26 | [@@mel.send.pipe: assertion]
#      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: `mel.send.pipe' has been removed. Use `@mel.send' with the `@mel.this` marker instead.

Looking at https://github.com/melange-re/melange/blob/main/Changes.md#501-53-2025-02-23
I see in 5.0.1-53 2025-02-23 BREAKING(ppx): remove @mel.send.pipe
and have therefore added "5.0.0" as an upper bound.

[anmonteiro]

thank you!

[shonfeder]

Only CI failures appear to be from missing sources. Thanks for the maintenance here!