Minor: Make messages consistent for LogicalPlan::Dml

[alamb]

Which issue does this PR close?

Follow on to #4902 from @avantgardnerio

Rationale for this change

There are some messages / display strings that appear to still reference an older version of the code

What changes are included in this PR?

Update the display name to Dml everywhere

Are these changes tested?

existing coverage

Are there any user-facing changes?

[avantgardnerio]

Thanks for catching this 🙌

[alamb]

Thanks for catching this 🙌

I figured this would be faster than going through another round of review on #4902

[ursabot]

Benchmark runs are scheduled for baseline = 4623166 and contender = 906896b. 906896b is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java