fishlim: Minor test improvements

- Don't have tests repeat themselves, meson has a `--repeat` flag
- Fix a minor leak of a GRand
- Speed up a test
- Increase timeout

This still needs a lot of improvements, it runs at lot of loops within
loops generating random strings that could be optimized. This means
it can take a very long time on some computers.

Closes #2629

plugins/fishlim/tests/meson.build

@@ -12,4 +12,5 @@ fishlim_tests = executable('fishlim_tests', fishlim_test_sources,
 
 test('Fishlim Tests', fishlim_tests,
   protocol: 'tap',
+  timeout: 600,
 )