convert file path to file uri in TestVerifiedHash

this uses filepath.ToSlash function to convert root of the filepath
to either slash or windows drive letter

it fixes the following unit test failure on windows:
```
=== RUN   TestVerifiedHash
    metadata_test.go:214:
        	Error Trace:	D:/a/crc/crc/pkg/crc/machine/bundle/metadata_test.go:214
        	            				D:/a/crc/crc/pkg/crc/machine/bundle/metadata_test.go:193
        	Error:      	Received unexpected error:
        	            	parse "file://D:\\a\\crc\\crc\\pkg\\crc\\machine\\bundle\\testdata\\sha256sum_correct_4.13.0.txt.sig": invalid port ":\\a\\crc\\crc\\pkg\\crc\\machine\\bundle\\testdata\\sha256sum_correct_4.13.0.txt.sig" after host
        	Test:       	TestVerifiedHash
```

pkg/crc/machine/bundle/metadata_test.go

@@ -209,5 +209,5 @@ func TestVerifiedHash(t *testing.T) {
 func testDataURI(t *testing.T, sha256sum string) string {
 	absPath, err := filepath.Abs(filepath.Join("testdata", sha256sum))
 	require.NoError(t, err)
-	return fmt.Sprintf("file:///%s", absPath)
+	return fmt.Sprintf("file://%s", filepath.ToSlash(absPath))
 }