Fix build with GCC 13 (add missing <cstdint> include)

GCC 13 (as usual for new compiler releases) shuffles around some
internal includes and so <cstdint> is no longer transitively included.

Explicitly include <cstdint> for uint64_t.

```
FAILED: src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o
/usr/lib/ccache/bin/g++-13  -I/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/.. -I/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1_build/generated-includes  -O2 -pipe
-march=native -fdiagnostics-color=always -frecord-gcc-switches -Wreturn-type -D_GLIBCXX_ASSERTIONS  -ggdb3 -fdiagnostics-color=always
-ffile-prefix-map=/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1=. -Wall -Wc++20-compat -Wcast-align -Wcatch-value -Wdeprecated -Wexceptions -Wextra -Wextra-semi -Wfloat-equal -Winit-self
-Wmisleading-indentation -Wmismatched-new-delete -Wmismatched-tags -Wmissing-braces -Wmissing-declarations -Wmissing-noreturn -Wnull-dereference -Wold-style-cast -Woverloaded-virtual -Wparentheses
-Wpedantic -Wreorder -Wshadow -Wstrict-aliasing -Wsuggest-override -Wundef -Wuninitialized -Wunreachable-code -Wunused -Wunused-function -Wunused-parameter -Wvla -MD -MT
src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o -MF src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o.d -o src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o -c
/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/internal/catch_clara.cpp
In file included from /var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/internal/catch_clara.cpp:12:
/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/../catch2/internal/catch_string_manip.hpp:47:14: error: 'uint64_t' in namespace 'std' does not name a type; did you mean 'wint_t'?
   47 |         std::uint64_t m_count;
      |              ^~~~~~~~
      |              wint_t
/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/../catch2/internal/catch_string_manip.hpp:51:42: error: expected ')' before 'count'
   51 |         constexpr pluralise(std::uint64_t count, StringRef label):
      |                            ~             ^~~~~~
      |                                          )
```

0 files changed, 0 insertions, 0 deletions