Update active settings in test cfg

[forsyth2]

Summary

Objectives:

• Fix active settings in pcmdi_diags task on test cfg so that it can be suppressed while testing other tasks.

Issue resolution:

• Resolves bug in test cfg found while testing Preserve legacy Xarray merge settings e3sm_diags#1016.

Select one: This pull request is...

• a bug fix: increment the patch version
• a small improvement: increment the minor version
• a new feature: increment the minor version
• an incompatible (non-backwards compatible) API change: increment the major version

Small Change

• To merge, I will use "Squash and merge". That is, this change should be a single commit.
• Logic: I have visually inspected the entire pull request myself.
• Pre-commit checks: All the pre-commits checks have passed.