Fix typo: MY_CXX_WARNING_FLGAS -> MY_CXX_WARNING_FLAGS in Cpp CMakeLists.txt

[arimu1]

Fixes #4864.

What

runtime/Cpp/CMakeLists.txt has two occurrences of a misspelled variable
reference, MY_CXX_WARNING_FLGAS, in the CMAKE_CXX_FLAGS_RELEASE lines
(one in the MSVC branch, one in the non-MSVC branch). The correctly spelled
variable is MY_CXX_WARNING_FLAGS.

This PR corrects both occurrences to MY_CXX_WARNING_FLAGS.

Why this is purely cosmetic

Since MY_CXX_WARNING_FLGAS was never defined, it silently expanded to
nothing in the set(CMAKE_CXX_FLAGS_RELEASE ...) lines — it did not cause a
build error. It also does not mean Release builds compile without
warning flags: line 89 (set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${MY_CXX_WARNING_FLAGS}")) already appends the warning flags to the base
CMAKE_CXX_FLAGS, and CMake concatenates CMAKE_CXX_FLAGS with the
per-config CMAKE_CXX_FLAGS_<CONFIG> variable when invoking the compiler.
So warning flags were already applied in Release builds through that path;
the typo only dropped a redundant second copy of the same flags being
appended a second time in the Release-specific line.

Notes

• Fixing the typo consistent with the correctly-spelled usage elsewhere in
  the same file (Debug, MinSizeRel, and RelWithDebInfo lines already use
  MY_CXX_WARNING_FLAGS correctly).
• No behavioral test added — this is a build-file wording/typo fix with no
  observable behavior change.
• A prior PR for the same issue, misspelled flag name MY_CXX_WARNING_FLGAS #4865, was opened and self-closed by the
  reporter without merging (it appears to have been opened from a branch
  literally named dev, against this repo's contribution guidelines). The
  typo is still present on current dev, so this PR supersedes it.

[arimu1]

C++ typo-only change (MY_CXX_WARNING_FLGAS → MY_CXX_WARNING_FLAGS). Rebased onto current dev.

Note: the red TypeScript build jobs look unrelated to this one-line CMake fix (cpp/java/js jobs green). Happy to dig if maintainers want, or they can ignore for this PR.