ci: fix remaining failing tests. Do mut ptr check only outside unsafe{} blocks.

vlib/v/checker/checker.v

@@ -1601,7 +1601,7 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 			if v := scope.find_var(ident.name) {
 				if left_first is ast.Ident {
 					assigned_var := left_first
-					if !v.is_mut && assigned_var.is_mut {
+					if !v.is_mut && assigned_var.is_mut && !c.inside_unsafe {
 						c.error('`$ident.name` is immutable, cannot have a mutable reference to it',
 							node.pos)
 					}

vlib/v/tests/ptr_arithmetic_test.v

@@ -1,18 +1,24 @@
 fn test_ptr_arithmetic(){
-	v := 4
-	mut p := &v
 	unsafe {
+		// Do NOT move this outside unsafe{}.
+		// It causes too much churn in CI when new checks are implemented.
+		// If you want to implement a specific failing test, do so inside
+		// vlib/v/checker/tests/ , NOT here.
+		v := 4
+		mut p := &v
 		p++
 		p += 2
 		p = p - 1
+		assert p == &v + 2
+		p = p + 1
+		assert p == &v + 3
+		r := p++
+		assert r == &v + 3
+		assert p == &v + 4
 	}
-	assert p == unsafe {&v + 2}
-	p = unsafe { p + 1 }
-	assert p == unsafe {&v + 3}
-	r := unsafe { p++ }
-	assert r == unsafe {&v + 3}
-	assert p == unsafe {&v + 4}
-	
+}
+
+fn test_ptr_arithmetic_over_byteptr() {	
 	// byteptr, voidptr, charptr are handled differently
 	mut q := byteptr(10)
 	unsafe {