It affected cmake-unity shared-curltool curldebug mingw-w64 gcc builds
when building the `testdeps` target.
Apply the solution already used in `lib/base64.c` and `lib/dynbuf.c`
to fix it.
Also update an existing GHA CI job to test the issue fixed.
```
In file included from curl/lib/version_win32.c:35,
from curl/_bld/src/CMakeFiles/curl.dir/Unity/unity_0_c.c:145:
curl/lib/memdebug.h:52:14: error: redundant redeclaration of 'curl_dbg_logfile' [-Werror=redundant-decls]
52 | extern FILE *curl_dbg_logfile;
| ^~~~~~~~~~~~~~~~
In file included from curl/src/slist_wc.c:32,
from curl/_bld/src/CMakeFiles/curl.dir/Unity/unity_0_c.c:4:
curl/lib/memdebug.h:52:14: note: previous declaration of 'curl_dbg_logfile' with type 'FILE *' {aka 'struct _iobuf *'}
52 | extern FILE *curl_dbg_logfile;
| ^~~~~~~~~~~~~~~~
curl/lib/memdebug.h:55:44: error: redundant redeclaration of 'curl_dbg_malloc' [-Werror=redundant-decls]
55 | CURL_EXTERN ALLOC_FUNC ALLOC_SIZE(1) void *curl_dbg_malloc(size_t size,
| ^~~~~~~~~~~~~~~
curl/lib/memdebug.h:55:44: note: previous declaration of 'curl_dbg_malloc' with type 'void *(size_t, int, const char *)' {aka 'void *(long long unsigned int, int, const char *)'}
55 | CURL_EXTERN ALLOC_FUNC ALLOC_SIZE(1) void *curl_dbg_malloc(size_t size,
| ^~~~~~~~~~~~~~~
[...]
curl/lib/memdebug.h:110:17: error: redundant redeclaration of 'curl_dbg_fclose' [-Werror=redundant-decls]
110 | CURL_EXTERN int curl_dbg_fclose(FILE *file, int line, const char *source);
| ^~~~~~~~~~~~~~~
curl/lib/memdebug.h:110:17: note: previous declaration of 'curl_dbg_fclose' with type 'int(FILE *, int, const char *)' {aka 'int(struct _iobuf *, int, const char *)'}
110 | CURL_EXTERN int curl_dbg_fclose(FILE *file, int line, const char *source);
| ^~~~~~~~~~~~~~~
```
Ref: https://ci.appveyor.com/project/curlorg/curl/builds/49840554/job/a4aoet17e9qnqx1a#L362
After: https://ci.appveyor.com/project/curlorg/curl/builds/49843735/job/hbo2uah2vj0ns523
Ref: #13689 (CI testing this PR with `DEBUGBUILD`/`CURLDEBUG`/shared-static combinations)
Depends-on: #13694
Depends-on: #13800Closes#13705
0fd794df35