Stop running client tests in parallel with xdist

These tests are pretty quick that they don't really benefit from xdist.
Plus not all of our tests are threadsafe (e.g. the ones that call
locale.setlocale()), so if there's no real need for parallelization,
let's skip it.

Refs #1880.

client/Makefile

@@ -56,8 +56,8 @@ TESTOPTS ?= -v --cov-config .coveragerc --cov-report html --cov-report term-miss
 RANDOM_SEED ?= $(shell bash -c 'echo $$RANDOM')
 
 .PHONY: test
-test: ## Run the application tests in parallel (for rapid development)
-	@TEST_CMD="poetry run pytest -v -n 4 --ignore=$(FTESTS) --ignore=$(ITESTS) $(TESTOPTS) $(TESTS)" ; \
+test: ## Run the application tests (for rapid development)
+	@TEST_CMD="poetry run pytest -v --ignore=$(FTESTS) --ignore=$(ITESTS) $(TESTOPTS) $(TESTS)" ; \
 		source scripts/setup-tmp-directories.sh; \
 		if command -v xvfb-run > /dev/null; then \
 		xvfb-run -a $$TEST_CMD ; else \
@@ -72,7 +72,7 @@ test-random: ## Run the application tests in random order
 
 .PHONY: test-integration
 test-integration: ## Run the integration tests
-	@TEST_CMD="poetry run pytest -v -n 4 $(ITESTS)" ; \
+	@TEST_CMD="poetry run pytest -v $(ITESTS)" ; \
 		if command -v xvfb-run > /dev/null; then \
 		xvfb-run -a $$TEST_CMD ; else \
 		$$TEST_CMD ; fi

client/pyproject.toml

@@ -41,7 +41,6 @@ pytest-mock = "*"
 pytest-qt = "^4.2.0"
 pytest-random-order = "*"
 pytest-vcr = "*"
-pytest-xdist = "^3.0.2"
 semgrep = "*"
 translate-toolkit = "*"
 types-polib = "*"