test: correct unhandled error events

build-request-file-object.test.js and get-content-type.test.js both make use of streams with non-existent paths to check errors. Possibly since upgrading jest these cause suites to fail with e.g.
```
Error: ENOENT: no such file or directory, open '/fake/path/custom-name.env'
Emitted 'error' event on ReadStream instance at:
    at emitErrorNT (node:internal/streams/destroy:157:8)
    at emitErrorCloseNT (node:internal/streams/destroy:122:3)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: '/fake/path/custom-name.env'
```

Since the errors are expected for these tests add a no-op handler to handle the error events.

test/unit/build-request-file-object.test.js

@@ -61,7 +61,8 @@ describe('buildRequestFileObject', () => {
     });
 
     it('should handle file object with a readable stream as its `value`', async () => {
-      const fileStream = fs.createReadStream(filepath);
+      // Note add an on error handler to avoid unhandled error events
+      const fileStream = fs.createReadStream(filepath).on('error', () => {});
       fileStream.path = `/fake/path/${customName}`;
 
       const fileParams = {
@@ -76,7 +77,8 @@ describe('buildRequestFileObject', () => {
     });
 
     it('should handle path property being a buffer', async () => {
-      const fileStream = fs.createReadStream(filepath);
+      // Note add an on error handler to avoid unhandled error events
+      const fileStream = fs.createReadStream(filepath).on('error', () => {});
       fileStream.path = Buffer.from(`/fake/path/${customName}`);
 
       const fileParams = {

test/unit/get-content-type.test.js

@@ -26,7 +26,8 @@ describe('getContentType', () => {
   });
 
   it('should not get content type from read stream with corrupted path property', async () => {
-    const streamFile = fs.createReadStream(filepath);
+    // Note add an on error handler to avoid unhandled error events
+    const streamFile = fs.createReadStream(filepath).on('error', () => {});
     streamFile.path = 'unrecognizeable-format';
     expect(await getContentType(streamFile)).toBeNull();
   });