Use separate opam cache for msys2 installs

Author: tobil4sk

dist/index.js

@@ -50,6 +50,7 @@ async function composeOpamCacheKeys() {
   const ocamlCompiler = await RESOLVED_COMPILER;
   const repositoryUrls = OPAM_REPOSITORIES.map(([_, value]) => value).join(",");
   const osInfo = await system.osInfo();
+  const msys2 = WINDOWS_ENVIRONMENT === "msys2" ? "msys2" : undefined;
   const plainKey = [
     PLATFORM,
     osInfo.release,
@@ -58,7 +59,9 @@ async function composeOpamCacheKeys() {
     ocamlCompiler,
     repositoryUrls,
     sandbox,
-  ].join(",");
+  ]
+    .concat(msys2 ?? [])
+    .join(",");
   const hash = crypto.createHash("sha256").update(plainKey).digest("hex");
   const key = `${CACHE_PREFIX}-setup-ocaml-opam-${hash}`;
   const restoreKeys = [key];