CompatHelper: bump compat for "PDMats" to "0.11"

[github-actions[bot]]

This pull request changes the compat entry for the PDMats package from 0.9, 0.10 to 0.9, 0.10, 0.11.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[coveralls]

Pull Request Test Coverage Report for Build 675

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 76.622%

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Totals
Change from base Build 635:	0.0%
Covered Lines:	1488
Relevant Lines:	1942

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💛 - Coveralls