ramus, tangra, flake: apply php backport overlay

Covers every PHP consumer: think/think-backend (php83) on ramus,
wordpress pools (pkgs.php) on tangra, and the perSystem think packages.

machines/ramus/think-greater-chiangmai.nix

@@ -54,7 +54,10 @@ in
     self.nixosModules.think-gtcm
     self.nixosModules.think-backend-gtcm
   ];
-  nixpkgs.overlays = [ self.overlays.packagesOverlay ];
+  nixpkgs.overlays = [
+    self.overlays.packagesOverlay
+    self.overlays.phpPr576853Overlay # TEMPORARY, see overlays/nixpkgs-pr-576853-php.nix
+  ];
 
   clan.core.vars.generators.greaterchiangmai = {
     files = {