ci: speed up nix build (#11697)

Signed-off-by: Antonio Nuno Monteiro <[email protected]>

Author: anmonteiro

.github/workflows/workflow.yml

@@ -118,23 +118,35 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v22
+      - uses: cachix/install-nix-action@v31
+        with:
+          extra_nix_config: |
+            extra-substituters = https://anmonteiro.nix-cache.workers.dev
+            extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
       - run: nix build
 
   fmt:
     name: Format
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v18
+      - uses: cachix/install-nix-action@v31
+        with:
+          extra_nix_config: |
+            extra-substituters = https://anmonteiro.nix-cache.workers.dev
+            extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
       - run: nix develop .#fmt -c make fmt
 
   doc:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v18
+      - uses: cachix/install-nix-action@v31
+        with:
+          extra_nix_config: |
+            extra-substituters = https://anmonteiro.nix-cache.workers.dev
+            extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
       - run: nix develop .#doc -c make doc
         env:
           LC_ALL: C
@@ -144,7 +156,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v22
+      - uses: cachix/install-nix-action@v31
+        with:
+          extra_nix_config: |
+            extra-substituters = https://anmonteiro.nix-cache.workers.dev
+            extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
       - run: nix develop .#coq -c make test-coq
         env:
           # We disable the Dune cache when running the tests
@@ -236,5 +252,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v22
+      - uses: cachix/install-nix-action@v31
+        with:
+          extra_nix_config: |
+            extra-substituters = https://anmonteiro.nix-cache.workers.dev
+            extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
       - run: nix develop .#microbench -c make dune build bench/micro