CI: Remove the pytest-xdist and pytest-rerunfailures plugins from the Benchmarks workflow

[seisman]

The Benchmarks workflow crashes frequently (e.g., https://github.com/GenericMappingTools/pygmt/actions/runs/9824664574/job/27124975569?pr=3310) after we added the pytest-xdist and pytest-rerunfailures plugins in #3193.

This PR removes the two plugins from the Benchmarks workflow.

[codspeed-hq]

CodSpeed Performance Report

Merging #3314 will degrade performances by 76.54%

_{Comparing ci/benchmark (f045638) with main (b907b4a)}

Summary

❌ 5 regressions
✅ 96 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	ci/benchmark	Change
❌	test_contour_matrix[DataFrame]	16.5 ms	69.1 ms	-76.06%
❌	test_contour_matrix[Dataset]	19 ms	71.5 ms	-73.49%
❌	test_contour_matrix[array]	16.1 ms	68.7 ms	-76.54%
❌	test_grdlandmask_no_outgrid	63.1 ms	130.9 ms	-51.83%
❌	test_sph2grd_no_outgrid	295.9 ms	408.5 ms	-27.56%