ci: set a ctest timeout of 1200 (20 minutes)

This should be long enough (with headroom) for our longest running tests,
which even under MSAN, TSAN, Valgrind, etc max out at about 800s.

i.e under Valgrind I see the longer runtimes as:
```bash
135/136 Test   #8: bench_sanity_check_high_priority .....   Passed  371.19 sec
136/136 Test #122: coinselector_tests ...................   Passed  343.39 sec
```

In the CI `tests` under TSAN:
```bash
tests ................................   Passed  795.20 sec
```
and MSAN:
```bash
tests ................................   Passed  658.48 sec
```

This will also prevent the current issue we are seeing of `ctest`
running until it reaches the CI timeout, see #30969.

However, we still need to figure out what underlying issue is causing
the tests to (sometimes) run for so long, but in the mean time, this
will stop `ctest` wasting our CI CPU.

ci/test/03_test_script.sh

@@ -146,7 +146,7 @@ if [ "$RUN_CHECK_DEPS" = "true" ]; then
 fi
 
 if [ "$RUN_UNIT_TESTS" = "true" ]; then
-  DIR_UNIT_TEST_DATA="${DIR_UNIT_TEST_DATA}" LD_LIBRARY_PATH="${DEPENDS_DIR}/${HOST}/lib" CTEST_OUTPUT_ON_FAILURE=ON ctest "${MAKEJOBS}"
+  DIR_UNIT_TEST_DATA="${DIR_UNIT_TEST_DATA}" LD_LIBRARY_PATH="${DEPENDS_DIR}/${HOST}/lib" CTEST_OUTPUT_ON_FAILURE=ON ctest "${MAKEJOBS}" --timeout $((TEST_RUNNER_TIMEOUT_FACTOR * 30 ))
 fi
 
 if [ "$RUN_UNIT_TESTS_SEQUENTIAL" = "true" ]; then