minor #28307 Mark ExceptionInterfaces throwable #2 (ostrolucky)

This PR was merged into the 4.2-dev branch.

Discussion
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Mark ExceptionInterfaces throwable #2

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This has been reverted in beta of 4.1 because of lack of support in prophecy, which has been fixed since then (incl. release). Can be merged again.

References:
symfony/symfony#26702
symfony/symfony#27420
symfony/symfony#27419
phpspec/prophecy#412

ping @dunglas @ciaranmcnulty @dkarlovi @Wirone @teohhanhui @stof @nicolas-grekas @ondrejmirtes

Commits
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17c3675226 Mark ExceptionInterfaces throwable

Exception/ExceptionInterface.php

@@ -16,6 +16,6 @@
  *
  * @author Jérôme Tamarelle <jerome@tamarelle.net>
  */
-interface ExceptionInterface
+interface ExceptionInterface extends \Throwable
 {
 }