CI: temporary pin of libyang to 3.0.18

There is ODR violation in libyang tests reported by ASan which breaks
our CI builds. This commit temporarily (until this gets solved in
upstream) pins the libyang version to 3.0.18 which builds just fine.

The log from ASan:

  52/60 Test #31: utest_plugins .....................***Failed    1.22 sec
  [==========] tests: Running 4 test(s).
  [ RUN      ] test_add_invalid
  [       OK ] test_add_invalid
  [ RUN      ] test_add_simple
  =================================================================
  ==2826==ERROR: AddressSanitizer: odr-violation (0x7f6d170dcb40):
    [1] size=24 'ly_version_so' /home/ci/src/cesnet-gerrit-public/github/CESNET/libyang/src/ly_common.c:43
    [2] size=24 'ly_version_so' /home/ci/src/cesnet-gerrit-public/github/CESNET/libyang/src/ly_common.c:43
  These globals were registered at these points:
    [1]:
      #0 0x437ffa in __asan_register_globals (/home/ci/build/github/CESNET/libyang/tests/utest_plugins+0x437ffa) (BuildId: e79d14f37e59b6533b66d19363b25fea9e324edb)
      #1 0x7f6d16691b9e in asan.module_ctor ly_common.c
      #2 0x7f6d1aad7236 in call_init /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-init.c:74:3
      #3 0x7f6d1aad7236 in call_init /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-init.c:26:1
      #4 0x7f6d1aad732c in _dl_init /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-init.c:121:5
      #5 0x7f6d1aad35c1 in _dl_catch_exception /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-catch.c:211:7
      #6 0x7f6d1aaddeeb in dl_open_worker /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-open.c:827:5
      #7 0x7f6d1aad3522 in _dl_catch_exception /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-catch.c:237:8
      #8 0x7f6d1aade2e3 in _dl_open /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-open.c:903:17
      #9 0x7f6d1a7b5713 in dlopen_doit /usr/src/debug/glibc-2.37-18.fc38.x86_64/dlfcn/dlopen.c:56:15
      #10 0x7f6d1aad3522 in _dl_catch_exception /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-catch.c:237:8
      #11 0x7f6d1aad3678 in _dl_catch_error /usr/src/debug/glibc-2.37-18.fc38.x86_64/elf/dl-catch.c:256:19
      #12 0x7f6d1a7b51f2 in _dlerror_run /usr/src/debug/glibc-2.37-18.fc38.x86_64/dlfcn/dlerror.c:138:17
      #13 0x7f6d1a7b57ce  /usr/src/debug/glibc-2.37-18.fc38.x86_64/dlfcn/dlopen.c:71:10
      #14 0x7f6d1a7b57ce in dlopen@@GLIBC_2.34 /usr/src/debug/glibc-2.37-18.fc38.x86_64/dlfcn/dlopen.c:81:12
      #15 0x485f82 in dlopen (/home/ci/build/github/CESNET/libyang/tests/utest_plugins+0x485f82) (BuildId: e79d14f37e59b6533b66d19363b25fea9e324edb)
      #16 0xcb5ee3 in plugins_load_module /home/ci/src/cesnet-gerrit-public/github/CESNET/libyang/src/plugins.c:378:17
      #17 0xcb5e67 in lyplg_add /home/ci/src/cesnet-gerrit-public/github/CESNET/libyang/src/plugins.c:589:11
      #18 0xea2a60 in test_add_simple /home/ci/src/cesnet-gerrit-public/github/CESNET/libyang/tests/utests/basic/test_plugins.c:50:5
      #19 0x7f6d1aac218f  (/lib64/libcmocka.so.0+0x618f) (BuildId: 785844a0941c0bde763740a981d056f60aa9c7b7)
      #20 0x7f6d1aac2904 in _cmocka_run_group_tests (/lib64/libcmocka.so.0+0x6904) (BuildId: 785844a0941c0bde763740a981d056f60aa9c7b7)
      #21 0xea21a2 in main /home/ci/src/cesnet-gerrit-public/github/CESNET/libyang/tests/utests/basic/test_plugins.c:152:12

Change-Id: Id8a4771296d2e85de2ec29fbd17046d280d2eda2

.zuul.yaml

@@ -4,13 +4,13 @@
         - f38-gcc-cover:
             required-projects:
               - name: github/CESNET/libyang
-                override-checkout: devel
+                override-checkout: cesnet/2024-07-08--3.0.18
               - name: github/onqtam/doctest
                 override-checkout: v2.3.6
         - f38-clang-asan-ubsan:
             required-projects: &projects
               - name: github/CESNET/libyang
-                override-checkout: devel
+                override-checkout: cesnet/2024-07-08--3.0.18
               - name: github/onqtam/doctest
                 override-checkout: v2.4.11
         - f38-clang-tsan: