chore: Pin CI dependencies

chore: Upgrade setup-ocaml
chore!: Drop support for OCaml 4.12

Author: ospencer

.github/workflows/esy.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-22.04, macos-latest, windows-latest]
 
     steps:
       - name: Setup node.js
@@ -29,7 +29,7 @@ jobs:
       # It also adds `shx` globally for cross-platform shell commands
       - name: Setup environment
         run: |
-          npm i -g esy
+          npm i -g esy@0.6.12
           npm i -g shx
 
       - name: Checkout project

.github/workflows/opam.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-22.04, macos-latest, windows-latest]
         ocaml-compiler: [4.12.1, 4.13.1, 4.14.1]
 
     steps: