build(ingest): pin mypy version

[hsheth2]

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[github-actions]

Unit Test Results (metadata ingestion)

       8 files  +       8         8 suites  +8   1h 2m 48s ⏱️ + 1h 2m 48s
   757 tests +   757     754 ✔️ +   754  3 💤 +3  0 ❌ ±0 
1 516 runs  +1 516  1 509 ✔️ +1 509  7 💤 +7  0 ❌ ±0 

Results for commit b6f4d43. ± Comparison against base commit 92192d2.

[github-actions]

Unit Test Results (build & test)

613 tests  +613   609 ✔️ +609   12m 9s ⏱️ + 12m 9s
151 suites +151       4 💤 +    4 
151 files   +151       0 ❌ ±    0 

Results for commit b6f4d43. ± Comparison against base commit 92192d2.

[treff7es]

lgtm