Rename RNDEP_VERSION to RN_DEP_VERSION (#51537)

Summary:
Pull Request resolved: #51537

To adhere more closely to our conventions, this change renames `RNDEP_VERSION` to `RN_DEP_VERSION`

## Changelog:
[Internal] -

Reviewed By: cortinico

Differential Revision: D75223248

fbshipit-source-id: 7ba44d7b358981bfbabe71c9876e3c865bdf9f50

Author: cipolleschi

packages/react-native/Package.swift

@@ -13,7 +13,7 @@ import PackageDescription
  To build React Native, you need to follow these steps:
  1. inside the `react-native` root folder, run `yarn install`
  2. `cd packages/react-native`
- 3. `RNDEP_VERSION=nightly HERMES_VERSION=nightly node scripts/prebuild-ios`
+ 3. `RN_DEP_VERSION=nightly HERMES_VERSION=nightly node scripts/prebuild-ios`
  4. `open Package.swift`
  5. Build in Xcode.
 

packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js

@@ -20,7 +20,7 @@ const dependencyLog = createLogger('ReactNativeDependencies');
 
 /**
  * Downloads ReactNativeDependencies artifacts from the specified version and build type. If you want to specify a specific
- * version of ReactNativeDependencies, use the RNDEP_VERSION environment variable. The path to the artifacts will be inside
+ * version of ReactNativeDependencies, use the RN_DEP_VERSION environment variable. The path to the artifacts will be inside
  * the packages/react-native/third-party folder.
  */
 async function prepareReactNativeDependenciesArtifactsAsync(
@@ -39,7 +39,7 @@ async function prepareReactNativeDependenciesArtifactsAsync(
   const versionFilePath = path.join(artifactsPath, 'version.txt');
 
   // Resolve the version from the environment variable or use the default version
-  let resolvedVersion = process.env.RNDEP_VERSION ?? version;
+  let resolvedVersion = process.env.RN_DEP_VERSION ?? version;
 
   if (resolvedVersion === 'nightly') {
     dependencyLog('Using latest nightly tarball');