test: fix _mm_log() prototypes
GCC 13 is unhappy to cast a MMLogLevel to a guint32:
[188/539] Compiling C object src/plugins/test-shared-icera.p/icera_tests_test-modem-helpers-icera.c.o
In file included from ../src/plugins/icera/tests/test-modem-helpers-icera.c:27:
../src/mm-log-test.h:25:1: warning: conflicting types for ‘_mm_log’ due to enum/integer mismatch; have ‘void(void *, const gchar *, const gchar *, const gchar *, guint32, const gchar *, ...)’ {aka ‘void(void *, const char *, const char *, const char *, unsigned int, const char *, ...)’} [-Wenum-int-mismatch]
25 | _mm_log (gpointer obj,
| ^~~~~~~
In file included from ../src/mm-log-test.h:20:
../src/mm-log.h:61:6: note: previous declaration of ‘_mm_log’ with type ‘void(void *, const gchar *, const gchar *, const gchar *, MMLogLevel, const gchar *, ...)’ {aka ‘void(void *, const char *, const char *, const char *, MMLogLevel, const char *, ...)’}
61 | void _mm_log (gpointer obj,
| ^~~~~~~
That's perfectly fine, just use the enum type directly.
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