patch 8.2.1619: Vim9: cannot pass "true" to spellsuggest()

Problem:    Vim9: cannot pass "true" to spellsuggest().
Solution:   Use tv_get_bool_chk(). (closes #6883)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index ea633c7..810769a 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -7828,7 +7828,7 @@
 		return;
 	    if (argvars[2].v_type != VAR_UNKNOWN)
 	    {
-		need_capital = (int)tv_get_number_chk(&argvars[2], &typeerr);
+		need_capital = (int)tv_get_bool_chk(&argvars[2], &typeerr);
 		if (typeerr)
 		    return;
 	    }