Only test the number of errors

The map implementation of go iterates a map random;y so we can't know
which error has what message.

It's ok to remove this here because we have an e2e test (the final
errors are sorted alphabetically).

Signed-off-by: Djordje Lukic <djordje.lukic@docker.com>

internal/validator/rules/externalsecrets_test.go

@@ -50,9 +50,6 @@ func TestExternalSecrets(t *testing.T) {
 
 		errs := s.Validate(input)
 		assert.Equal(t, len(errs), 2)
-
-		assert.ErrorContains(t, errs[0], `secret "my_secret" should be external`)
-		assert.ErrorContains(t, errs[1], `secret "my_other_secret" should be external`)
 	})
 
 }