CompatHelper: add new compat entry for MarginalLogDensities at version 0.4 for package test, (keep existing compat)

[github-actions]

This pull request sets the compat entry for the MarginalLogDensities package to 0.4 for package test.
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.
Note: Consider registering a new release of your package immediately after merging this PR, as downstream packages may depend on this for tests to pass.

[github-actions]

Benchmark Report for Commit b912ae9

Computer Information

Julia Version 1.11.7
Commit f2b3dbda30a (2025-09-08 12:10 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 4 × AMD EPYC 7763 64-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, znver3)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)

Benchmark Results

┌───────────────────────┬───────┬─────────────┬───────────────────┬────────┬────────────────┬─────────────────┐
│                 Model │   Dim │  AD Backend │           VarInfo │ Linked │ t(eval)/t(ref) │ t(grad)/t(eval) │
├───────────────────────┼───────┼─────────────┼───────────────────┼────────┼────────────────┼─────────────────┤
│ Simple assume observe │     1 │ forwarddiff │             typed │  false │            8.6 │             1.6 │
│           Smorgasbord │   201 │ forwarddiff │             typed │  false │          674.5 │            42.0 │
│           Smorgasbord │   201 │ forwarddiff │ simple_namedtuple │   true │          444.9 │            51.2 │
│           Smorgasbord │   201 │ forwarddiff │           untyped │   true │         1170.7 │            31.1 │
│           Smorgasbord │   201 │ forwarddiff │       simple_dict │   true │         6927.3 │            29.8 │
│           Smorgasbord │   201 │ reversediff │             typed │   true │         1481.7 │            29.0 │
│           Smorgasbord │   201 │    mooncake │             typed │   true │         1043.7 │             4.5 │
│    Loop univariate 1k │  1000 │    mooncake │             typed │   true │         5935.8 │             4.3 │
│       Multivariate 1k │  1000 │    mooncake │             typed │   true │         1016.6 │             9.0 │
│   Loop univariate 10k │ 10000 │    mooncake │             typed │   true │        66846.1 │             4.1 │
│      Multivariate 10k │ 10000 │    mooncake │             typed │   true │         8524.9 │            10.0 │
│               Dynamic │    10 │    mooncake │             typed │   true │          141.4 │            10.8 │
│              Submodel │     1 │    mooncake │             typed │   true │           12.1 │             5.1 │
│                   LDA │    12 │ reversediff │             typed │   true │          996.8 │             2.1 │
└───────────────────────┴───────┴─────────────┴───────────────────┴────────┴────────────────┴─────────────────┘