Disable terminal logger experience for dotnet test in manual tests. (#100333)

Author: nohwnd

src/libraries/System.Console/tests/ManualTests/Readme.md

@@ -6,7 +6,8 @@ To run the suite, follow these steps:
 1. Build the CLR and libraries.
 2. Using a terminal, navigate to the current folder.
 3. Enable manual testing by defining the `MANUAL_TESTS` environment variable (e.g. on bash `export MANUAL_TESTS=true`).
-4. Run `dotnet test` and follow the instructions in the command prompt.
+4. Disable terminal logger output for dotnet test by setting `MSBUILDENSURESTDOUTFORTASKPROCESSES=1` environment variable. (e.g. on bash `export MSBUILDENSURESTDOUTFORTASKPROCESSES=1`).
+5. Run `dotnet test` and follow the instructions in the command prompt.
 
 ## Instructions for Windows testers