Make dev-requirements.txt look like other repos and work with update_dev_dependency_branches.sh

[gshank]

Problem

When updating the integration.yml workflow, updating dbt-core branch didn't work because the format in dev-requirements.txt didn't match what was expected in update_dev_dependency_branches.sh

Solution

Add the "#egg" snippet that the other repos have and that update_dev_dependency_branches.sh expects.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX