acknowledge it won't work on 18.x

Author: aduh95

README.md

@@ -306,6 +306,8 @@ same major line. Should you need to upgrade to a new major, use an explicit
 
 - `COREPACK_ENV_FILE` can be set to `0` to request Corepack to not attempt to
   load `.corepack.env`; it can be set to a path to specify a different env file.
+  For Node.js 18.x users, this setting has no effect as that version doesn't
+  support parsing of `.env` files.
 
 ## Troubleshooting
 

tests/main.test.ts

@@ -314,7 +314,10 @@ it(`should use hash from env even when "devEngines" defines a different one`, as
   });
 });
 
-it(`should use hash from env even when ".corepack.env" defines a different one`, async () => {
+it(`should use hash from env even when ".corepack.env" defines a different one`, async t => {
+  // Skip rest of the test on Node.js 18.x as it lacks support for .env files.
+  if (process.version.startsWith(`v18.`)) t.skip();
+
   await xfs.mktempPromise(async cwd => {
     await xfs.writeJsonPromise(ppath.join(cwd, `package.json` as PortablePath), {
       devEngines: {
@@ -336,7 +339,10 @@ it(`should use hash from env even when ".corepack.env" defines a different one`,
 });
 
 describe(`should accept range in devEngines only if a specific version is provided`, () => {
-  it(`either in .corepack.env`, async() => {
+  it(`either in .corepack.env`, async t => {
+    // Skip rest of the test on Node.js 18.x as it lacks support for .env files.
+    if (process.version.startsWith(`v18.`)) t.skip();
+
     await xfs.mktempPromise(async cwd => {
       await xfs.writeJsonPromise(ppath.join(cwd, `package.json` as PortablePath), {
         devEngines: {
@@ -361,7 +367,10 @@ describe(`should accept range in devEngines only if a specific version is provid
       });
     });
   });
-  it(`either in a different env file specified in env`, async() => {
+  it(`either in a different env file specified in env`, async t => {
+    // Skip rest of the test on Node.js 18.x as it lacks support for .env files.
+    if (process.version.startsWith(`v18.`)) t.skip();
+
     await xfs.mktempPromise(async cwd => {
       await xfs.writeJsonPromise(ppath.join(cwd, `package.json` as PortablePath), {
         devEngines: {
@@ -445,7 +454,10 @@ describe(`should accept range in devEngines only if a specific version is provid
   });
 });
 
-it(`Should use version from correct source`, async () => {
+it(`Should use version from correct source`, async t => {
+  // Skip rest of the test on Node.js 18.x as it lacks support for .env files.
+  if (process.version.startsWith(`v18.`)) t.skip();
+
   await xfs.mktempPromise(async cwd => {
     await xfs.writeJsonPromise(ppath.join(cwd, `package.json` as PortablePath), {
       devEngines: {
@@ -484,7 +496,10 @@ it(`Should use version from correct source`, async () => {
 });
 
 describe(`should reject if range in devEngines does not match version provided`,  () => {
-  it(`in .corepack.env`, async () => {
+  it(`in .corepack.env`, async t => {
+    // Skip rest of the test on Node.js 18.x as it lacks support for .env files.
+    if (process.version.startsWith(`v18.`)) t.skip();
+
     await xfs.mktempPromise(async cwd => {
       await xfs.writeJsonPromise(ppath.join(cwd, `package.json` as PortablePath), {
         devEngines: {