patch 8.2.0155: warnings from MinGW compiler; tests fail without +float

Problem:    Warnings from MinGW compiler. (John Marriott) Json test fails when
            building without +float feature.
Solution:   Init variables. Fix Json parsing. Skip a few tests that require
            the +float feature.
diff --git a/src/vim9script.c b/src/vim9script.c
index fb19258..9aa33d0 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -323,6 +323,7 @@
 		    *arg = cc;
 		    return NULL;
 		}
+		ufunc = NULL;
 	    }
 	    else
 	    {
@@ -355,6 +356,7 @@
 		    *arg = cc;
 		    return NULL;
 		}
+		sv = NULL;
 	    }
 
 	    imported = new_imported(gap != NULL ? gap