disable trace output for commands run in get_source_tarball_from_git

[boegel]

This fixes test_get_source_tarball_from_git when the test is not skipped sicne a GitHub token is available, which is broken because of the additional trace output (caused by enabling --trace by default in #4250):

FAIL: test_get_source_tarball_from_git (test.framework.filetools.FileToolsTest)
Test get_source_tarball_from_git function.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/runner/405fb0cc2a0118c1b3f4332611c244409b9d3fa5/lib/python3.6/site-packages/test/framework/filetools.py", line 2782, in test_get_source_tarball_from_git
    run_check()
  File "/tmp/runner/405fb0cc2a0118c1b3f4332611c244409b9d3fa5/lib/python3.6/site-packages/test/framework/filetools.py", line 2765, in run_check
    self.assertTrue(regex.search(stdout), "Pattern '%s' found in: %s" % (regex.pattern, stdout))
AssertionError: None is not true : Pattern '  running command "git clone --depth 1 --branch tag_for_tests git@github.com:easybuilders/testrepository.git"
  \(in .*/tmp.*\)
  running command "tar cfvz .*/target/test.tar.gz --exclude .git testrepository"
  \(in .*/tmp.*\)' found in:   >> running command:
	[started at: 2023-08-06 16:53:17]
	[working dir: /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/tmpp_ixh545]
	[output logged in /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/easybuild-run_cmd-vtki1hp8.log]
	git clone --depth 1 --branch tag_for_tests git@github.com:easybuilders/testrepository.git
  running command "git clone --depth 1 --branch tag_for_tests git@github.com:easybuilders/testrepository.git"
  (in /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/tmpp_ixh545)
  >> running command:
	[started at: 2023-08-06 16:53:17]
	[working dir: /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/tmpp_ixh545]
	[output logged in /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/easybuild-run_cmd-l1po41__.log]
	tar cfvz /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/target/test.tar.gz --exclude .git testrepository
  running command "tar cfvz /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/target/test.tar.gz --exclude .git testrepository"
  (in /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/tmpp_ixh545)
directory /tmp/eb-edjcffb7/eb-4r4ias8b/eb-sq9lqq1o/eb-p08iwl5l/eb-yovari1d/tmpp_ixh545 removed