(test) fix: rename SIZEOF_LONG to SENTRY_SIZEOF_LONG

[JoshuaMoelans]

Fixes #1810

#skip-changelog

[jpnurmi]

The problem is that ansel sets CMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY globally, which breaks CheckTypeSize so renaming the output variable doesn't help:

In file included from C:/msys64/home/jpnurmi/ansel/src/external/sentry-native/src/sentry_core.c:22:
C:/msys64/home/jpnurmi/ansel/src/external/sentry-native/src/sentry_sync.h:376:28: error: invalid token at start of a preprocessor expression
  376 | #    if SENTRY_SIZEOF_LONG == 8
      |                            ^
C:/msys64/home/jpnurmi/ansel/src/external/sentry-native/src/sentry_sync.h:390:28: error: invalid token at start of a preprocessor expression
  390 | #    if SENTRY_SIZEOF_LONG == 8
      |                            ^
C:/msys64/home/jpnurmi/ansel/src/external/sentry-native/src/sentry_sync.h:421:28: error: invalid token at start of a preprocessor expression
  421 | #    if SENTRY_SIZEOF_LONG == 8
      |                            ^
3 errors generated.

I think we should not have a workaround in sentry-native because it would break any other project relying on CheckTypeSize. I sent a proposal to fix on their side instead:

• build: scope static CMake flag probes aurelienpierreeng/ansel#997