Update def to class typo in actors docs

[pfackeldey]

A small typo fix for the documentation of Actors.

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    27 files  ±0      27 suites  ±0   11h 16m 53s ⏱️ + 4m 58s
 4 115 tests ±0   4 002 ✅ ±0    111 💤 ±0  2 ❌ +1 
51 595 runs   - 1  49 309 ✅ ±0  2 284 💤  - 1  2 ❌ +1 

For more details on these failures, see this check.

Results for commit 6fe9bcd. ± Comparison against base commit 966ec61.

[jrbourbeau]

Good catch, thanks @pfackeldey