Bump StackExchange.Redis from 3.1.13 to 3.1.31

[mgravell]

Routine bump of the core dependency, with the analyzer surface as the motivation.

3.1.31 adds four new analyzer rules over 3.1.13:

• SER305 - awaiting a queued command before Execute, which will never complete
• SER306 - awaiting a fire-and-forget result, which yields nothing
• SER307 - blocking on a redis call instead of awaiting it
• SER308 - blocking on a task through the library's Wait helpers

It also ships a StackExchange.Redis.CodeFixes.dll alongside the existing analyzer assembly, so some of these come with fixes attached.

None of the new rules fire here: the build is clean, 0 warnings, 0 errors, across net481 / netstandard2.0 / net6.0 / net8.0 / net10.0 plus the test and Doc projects. Verified the analyzer is actually loaded and reporting rather than silently absent - a throwaway probe project on 3.1.31 does produce SER307 for db.StringGetAsync(...).Result. The .Result uses in our tests don't trip it because they go through a local rather than being applied to the invocation directly.

Also rebuilt with every SER3xx escalated to warning (they are not all warning-by-default) - still nothing.

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Note

Low Risk
Patch-level dependency bump only; no application code or API surface changes in this repo.

Overview
Bumps the central StackExchange.Redis package version from 3.1.13 to 3.1.31 in Directory.Packages.props.

The newer package adds analyzer rules SER305–SER308 (mis-await / blocking Redis usage) plus code fixes. No other files change.

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