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

[github-actions]

This pull request sets the compat entry for the MarginalLogDensities package to 0.4 for package docs.
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 7d78491

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 × Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, icelake-server)
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 │            8.1 │             1.6 │
│           Smorgasbord │   201 │ forwarddiff │             typed │  false │          624.3 │            41.0 │
│           Smorgasbord │   201 │ forwarddiff │ simple_namedtuple │   true │          390.6 │            57.6 │
│           Smorgasbord │   201 │ forwarddiff │           untyped │   true │         1092.0 │            31.5 │
│           Smorgasbord │   201 │ forwarddiff │       simple_dict │   true │         6071.8 │            29.2 │
│           Smorgasbord │   201 │ reversediff │             typed │   true │         1283.5 │            31.6 │
│           Smorgasbord │   201 │    mooncake │             typed │   true │          977.4 │             4.4 │
│    Loop univariate 1k │  1000 │    mooncake │             typed │   true │         4921.3 │             4.8 │
│       Multivariate 1k │  1000 │    mooncake │             typed │   true │         1133.9 │             7.2 │
│   Loop univariate 10k │ 10000 │    mooncake │             typed │   true │        54329.9 │             4.4 │
│      Multivariate 10k │ 10000 │    mooncake │             typed │   true │        10901.2 │             7.6 │
│               Dynamic │    10 │    mooncake │             typed │   true │          135.1 │             7.6 │
│              Submodel │     1 │    mooncake │             typed │   true │           13.3 │             4.3 │
│                   LDA │    12 │ reversediff │             typed │   true │          856.2 │             2.1 │
└───────────────────────┴───────┴─────────────┴───────────────────┴────────┴────────────────┴─────────────────┘