test_gdbprinters: don't crash after running for >= 60 seconds

All 27 gdbprinters test cases pass on my computer, but they run for
slightly longer than a minute. Thus a regular crash on exit, which ctest
reports as an overall test failure.

Such a crash during a slow KDevelop startup was fixed in the same way in
43db1a72.

CCBUG: 425841
1 job for !192 with fix-60-second-test_gdpbrinters-crash in 33 minutes and 23 seconds
detached
Status Job ID Name Coverage
  Build
passed #77457
linux kf5-qt5 qt5.12

00:33:23

47.0%