Update TraceEvent to 3.2.8 for LTTng PGO mappings

[benaadams]

Update TraceEventVersion from 3.1.28 to 3.2.8 so dotnet-pgo consumes the released LTTng CTF mappings for MethodDetails and MethodILToNativeMap_V1 from microsoft/perfview#2392. The fix is included in PerfView and TraceEvent 3.2.8, removing the release blocker identified in the issue discussion.

Resolves #125883.

This updates the shared dependency used by runtime tools and tests. The separate Linux CPU-sample conversion work tracked in microsoft/perfview#2393 and #125932 remains outside this change.

Validation:

• Release builds of dotnet-pgo, PdbChecker, R2RTest, and DependencyGraphViewer: zero warnings or errors.
• All seven dotnet-pgo tests pass with the xUnit console runner.
• A package mapping check fails with 3.1.28 (neither required mapping present) and passes with 3.2.8: MethodDetails uses opcode 43 / event ID 72 / version 0; MethodILToNativeMap_V1 uses opcode 87 / event ID 190 / version 1.
• Full Linux perfcollect/SPGO collection was not rerun.

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