test: skip flaky tests

test/functional/lua/watch_spec.lua

@@ -31,6 +31,7 @@ describe('vim._watch', function()
       end
 
       if watchfunc == 'watch' then
+        skip(is_os('mac'), 'flaky test on mac')
         skip(is_os('bsd'), 'Stopped working on bsd after 3ca967387c49c754561c3b11a574797504d40f38')
       else
         skip(

test/unit/eval/typval_spec.lua

@@ -3352,7 +3352,7 @@ describe('typval.c', function()
         end
       end
       describe('string()', function()
-        itp('works', function()
+        pending('works (skip due to flakiness)', function()
           local buf = lib.tv_get_string(lua2typvalt(int(1)))
           local buf_chk = lib.tv_get_string_chk(lua2typvalt(int(1)))
           neq(buf, buf_chk)