[test] Drop the arm valgrind gate on the concurrency tests

[aaronj0]

Now that our valgrind ARM issues are solved, revert #19

[github-actions]

Test Results

Configuration	Result
macos-26-intel-llvm21-py3.14-cxx20	= 437 passed, 44 skipped, 85 xfailed, 32 xpassed, 100 warnings in 93.45s (0:01:33) =
macos-26-llvm21-py3.14-cxx20	==== 438 passed, 37 skipped, 93 xfailed, 30 xpassed, 100 warnings in 51.36s ====
ubuntu-24.04-llvm21-py3.14-cxx20-vg	====== 553 passed, 25 skipped, 18 xfailed, 2 xpassed in 104.58s (0:01:44) ======
ubuntu-24.04-llvm22-py3.14-cxx20	====== 553 passed, 25 skipped, 19 xfailed, 1 xpassed in 110.43s (0:01:50) ======
ubuntu-24.04-llvm22-py3.14-cxx20-cling	====== 543 passed, 25 skipped, 27 xfailed, 3 xpassed in 93.01s (0:01:33) =======
ubuntu-24.04-llvm22-py3.14-cxx23	====== 574 passed, 3 skipped, 20 xfailed, 1 xpassed in 113.43s (0:01:53) =======