Produce a clearer error message when file is not installed

lib/actions-util.js

@@ -387,11 +387,19 @@ exports.getWorkflowRunAttempt = getWorkflowRunAttempt;
 const getFileType = async (filePath) => {
     let stderr = "";
     let stdout = "";
+    let fileCmdPath;
+    try {
+        fileCmdPath = await safeWhich.safeWhich("file");
+    }
+    catch (e) {
+        core.info("The `file` program is required, but does not appear to be installed. Please install it.");
+        throw e;
+    }
     try {
         // The `file` command will output information about the type of file pointed at by `filePath`.
         // For binary files, this may include e.g. whether they are static of dynamic binaries.
         // The `-L` switch instructs the command to follow symbolic links.
-        await new toolrunner.ToolRunner(await safeWhich.safeWhich("file"), ["-L", filePath], {
+        await new toolrunner.ToolRunner(fileCmdPath, ["-L", filePath], {
             silent: true,
             listeners: {
                 stdout: (data) => {