CI/GCC: Add Fedora 44, fix build errors and threadsappend

- Add Fedora 44 to CI tests
- Fix build issues from the newer compiler. These are mostly 'char *'
  to 'const char *' conversions.
- Fix threadsappend.c test waiting for the same thread TID twice.
  This caused the test to hang on F44 (but strangely not other OSs?)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #18478

module/nvpair/nvpair.c

@@ -1923,8 +1923,9 @@ nvlist_lookup_nvpair_ei_sep(nvlist_t *nvl, const char *name, const char sep,
 {
 	nvpair_t	*nvp;
 	const char	*np;
-	char		*sepp = NULL;
-	char		*idxp, *idxep;
+	const char	*sepp = NULL;
+	const char	*idxp;
+	char		*idxep;
 	nvlist_t	**nva;
 	long		idx = 0;
 	int		n;