Add required javascript file to fix dry run script

[markhallen]

What are you trying to accomplish?

When splitting up PRs for the introduction of the bun ecosystem we missed a required file in the first PR.

Resolves #11483

How will you know you've accomplished your goal?

The dry run script should no longer raise an error when it encounters the line require "dependabot/javascript" in bin/dry-run.rb:114.

[dependabot-core-dev] ~ $ ./bin/dry-run.rb 
usage: ruby bin/dry-run.rb [OPTIONS] PACKAGE_MANAGER REPO
        --provider PROVIDER          SCM provider e.g. github, azure, bitbucket
        --dir DIRECTORY              Dependency file directory
        --branch BRANCH              Repo branch
        --dep DEPENDENCIES           Comma separated list of dependencies to update
        --cache STEPS                Cache e.g. files, dependencies
        --write                      Write the update to the cache directory
        --reject-external-code       Reject external code
        --requirements-update-strategy STRATEGY
                                     Options: lockfile_only, auto, widen_ranges, bump_versions or bump_versions_if_necessary
        --commit COMMIT              Commit to fetch dependency files from
        --vendor-dependencies        Vendor dependencies
        --updater-options OPTIONS    Comma separated list of updater options, available options depend on PACKAGE_MANAGER
        --security-updates-only      Only update vulnerable dependencies
        --profile                    Profile using Stackprof. Output in `tmp/stackprof-<datetime>.dump`
        --pull-request               Output pull request information metadata: title, description
        --enable-beta-ecosystems     Enable beta ecosystems
[dependabot-core-dev] ~ $ 

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.