Merge branch 'develop-bump-what4-dependency'. Close #514.

**Description**

`what4` has seen a new release 1.6, but `copilot-theorem` needs versions
strictly lower than 1.6. This version is API-compatible for all features
used by `copilot-theorem`, but it includes support for GHC 9.8, which we
want to also support.

**Type**

- Management: update versions of dependencies.

**Additional context**

None.

**Requester**

- Ryan Scott.

**Method to check presence of bug**

The following dockerfile installs copilot forcing the use of what4-1.6,
in which case it prints the message "Success".

```
FROM ubuntu:focal

RUN apt-get update

RUN apt-get install --yes libz-dev
RUN apt-get install --yes git

RUN apt-get install --yes wget
RUN mkdir -p $HOME/.ghcup/bin
RUN wget https://downloads.haskell.org/~ghcup/0.1.19.2/x86_64-linux-ghcup-0.1.19.2 -O $HOME/.ghcup/bin/ghcup

RUN chmod a+x $HOME/.ghcup/bin/ghcup
ENV PATH=$PATH:/root/.ghcup/bin/
ENV PATH=$PATH:/root/.cabal/bin/
RUN apt-get install --yes curl
RUN apt-get install --yes gcc g++ make libgmp3-dev

SHELL ["/bin/bash", "-c"]

RUN ghcup install ghc 9.4
RUN ghcup install cabal 3.8
RUN ghcup set ghc 9.4.8
RUN cabal update

CMD git clone $REPO \
    && cd $NAME \
    && git checkout $COMMIT \
    && cabal install --lib copilot**/ \
         --constraint="what4>=1.6" \
    && echo Success
```

Command (substitute variables based on new path after merge):
```
$ docker run -e "REPO=https://github.com/Copilot-Language/copilot" -e "NAME=copilot" -e "COMMIT=<HASH>" -it copilot-verify-514
```

**Expected result**

Executing the image above prints the message "Success", indicating that
Copilot can be installed with `what4-1.6`.

**Solution implemented**

Modify `copilot-theorem`'s cabal file to _also_ accept `what4` versions
`>= 1.6` and `<1.7`.

No other changes needed to `copilot-theorem` to work with that version
of `what4`.

**Further notes**

None.

Author: ivanperez-keera

copilot-theorem/CHANGELOG

@@ -1,3 +1,6 @@
+2024-07-06
+        * What4 upper-bound dependency version bump. (#514)
+
 2024-05-07
         * Version bump (3.19.1). (#512)
         * Fix handling of unsatisfiable properties with Kind2. (#495)

copilot-theorem/copilot-theorem.cabal

@@ -61,7 +61,7 @@ library
                           , random                >= 1.1 && < 1.3
                           , transformers          >= 0.5 && < 0.7
                           , xml                   >= 1.3 && < 1.4
-                          , what4                 >= 1.3 && < 1.6
+                          , what4                 >= 1.3 && < 1.7
 
                           , copilot-core          >= 3.19.1 && < 3.20
                           , copilot-prettyprinter >= 3.19.1 && < 3.20