Improve output for missing required plugins/unknown config keys (#7723)

Co-authored-by: Florian Bruhin <me@the-compiler.org>

changelog/7572.improvement.rst

@@ -0,0 +1 @@
+When a plugin listed in ``required_plugins`` is missing, a simple error message is now shown instead of a stacktrace.

src/_pytest/config/__init__.py

@@ -1174,9 +1174,8 @@ class Config:
                 missing_plugins.append(required_plugin)
 
         if missing_plugins:
-            fail(
+            raise UsageError(
                 "Missing required plugins: {}".format(", ".join(missing_plugins)),
-                pytrace=False,
             )
 
     def _warn_or_fail_if_strict(self, message: str) -> None:

testing/test_config.py

@@ -362,7 +362,7 @@ class TestParseIni:
         testdir.makeini(ini_file_text)
 
         if exception_text:
-            with pytest.raises(pytest.fail.Exception, match=exception_text):
+            with pytest.raises(pytest.UsageError, match=exception_text):
                 testdir.parseconfig()
         else:
             testdir.parseconfig()