Enforce repo-review rule PP308

PP308: Specifies useful pytest summary

An explicit summary flag like `-ra` should be in `addopts = [...]` (print
summary of all fails/errors).

pyproject.toml

@@ -68,7 +68,7 @@ repository = "https://github.com/ImagingDataCommons/highdicom.git"
 
 [tool.pytest.ini_options]
 minversion = "7"
-addopts = ["--doctest-modules", "--strict-config", "--strict-markers"]
+addopts = ["--doctest-modules", "-ra", "--strict-config", "--strict-markers"]
 testpaths = ["tests"]
 log_cli_level = "INFO"
 xfail_strict = true