ci: expose env vars in GitHub workflow

test: add explanatory code comments in fork test

.github/workflows/ci.yml

@@ -1,7 +1,11 @@
 name: "CI"
 
 env:
+  ALCHEMY_API_KEY: ${{ secrets.ALCHEMY_API_KEY }}
+  ETHERSCAN_API_KEY: ${{ secrets.ETHERSCAN_API_KEY }}
   FOUNDRY_PROFILE: "ci"
+  INFURA_API_KEY: ${{ secrets.INFURA_API_KEY }}
+  MNEMONIC: ${{ secrets.MNEMONIC }}
 
 on:
   pull_request:

test/Foo.t.sol

@@ -33,9 +33,12 @@ contract FooTest is PRBTest, StdCheats {
     /// for this test to run - you can get an API key for free at https://alchemy.com.
     function testFork_Example() external {
         string memory alchemyApiKey = vm.envOr("ALCHEMY_API_KEY", string(""));
+        // Silently pass this test if the user didn't define the API key.
         if (bytes(alchemyApiKey).length == 0) {
             return;
         }
+
+        // Run the test normally, otherwise.
         vm.createSelectFork({urlOrAlias: "ethereum", blockNumber: 16_428_000});
         address usdc = 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48;
         address holder = 0x7713974908Be4BEd47172370115e8b1219F4A5f0;