DCM checks on CI do not match local analysis errors

[kenzieschmoll]

Here is an example check that failed on the CI when I had no warnings locally
https://github.com/flutter/devtools/actions/runs/6113696534/job/16593734734

[elliette]

I'm guessing this is because we weren't pinning the DCM version, which should now be fixed: #6703