Fixes #9687. This PR will make cabal-install use the default cabal spec version for cabal init -n when no --cabal-version=spec_ver is passed. Previously, the version was retrieved at runtime by calling cabal --version and it was assumed that the cabal executable exists in PATH for it to work without returning an error.

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added. (Ask for help if you don’t know how to write them! Ask for an exemption if tests are too complex for too little coverage!)

QA Notes

Calling /path/to/cabal init -n whenever the cabal executable is not in PATH should correctly initialize a cabal project in the current directory without throwing an exception or returning an error.

• In the generated .cabal file, the cabal-version key value must be the default Cabal specification version, similar to that if cabal init -n --simple was used instead. Currently, the current default spec version is 3.0.