Cannot run tests in VSCode UI: module Plug.Builder is not loaded

I have a problem when attempting to run a test inside of the VSCode (i.e. by clicking on a green triangle to the left of the test). The output I get in the debug window:

Started ElixirLS Debug Adapter v0.23.0
ElixirLS Debug Adapter built with elixir "1.17.2" on OTP "27"
Running on elixir "1.17.2 (compiled with Erlang/OTP 27)" on OTP "27"
Protocols are not consolidated
Starting debugger in directory: /home/ought/Coding/Elixir/sample_app
Running with MIX_ENV: test MIX_TARGET: host
Compiling 23 files (.ex)
    error: module Plug.Builder is not loaded and could not be found. This may be happening because the module you are trying to load directly or indirectly depends on the current module
    │
  2 │   use Phoenix.Endpoint, otp_app: :sample_app
    │   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    │
    └─ lib/sample_app_web/endpoint.ex:2: SampleAppWeb.Endpoint (module)

== Compilation error in file lib/sample_app_web/endpoint.ex ==
** (CompileError) lib/sample_app_web/endpoint.ex: cannot compile module SampleAppWeb.Endpoint (errors have been logged)
    (elixir 1.17.2) expanding macro: Kernel.use/2
    lib/sample_app_web/endpoint.ex:2: SampleAppWeb.Endpoint (module)
    (phoenix 1.7.14) expanding macro: Phoenix.Endpoint.__using__/1
    lib/sample_app_web/endpoint.ex:2: SampleAppWeb.Endpoint (module)
    (elixir 1.17.2) expanding macro: Kernel.use/2

This problem does not happen when I run the tests from the terminal window by mix test - this way tests work normally.
My tasks are the default ones - i.e.:

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "mix_task",
            "name": "mix (Default task)",
            "request": "launch",
            "projectDir": "${workspaceRoot}"
        },
        {
            "type": "mix_task",
            "name": "mix test",
            "request": "launch",
            "task": "test",
            "taskArgs": [
                "--trace"
            ],
            "startApps": true,
            "projectDir": "${workspaceRoot}",
            "requireFiles": [
                "test/**/test_helper.exs",
                "test/**/*_test.exs"
            ]
        }
    ]
}

The repository of my simple project is here: https://github.com/StragaSevera/sample_app . The extension that I use is ElixirLS.
Is there any way to make this feature (running tests in IDE) work? It’s a dealbreaker for me =-)