[Intl] Fixed tests failing on PHP 5.5
Removed PHP 5.5 from the allowed failures.
merged branch jakzal/2.3-tests-on-php-5.5 (PR #8324)

This PR was merged into the 2.3 branch.

Discussion
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[Intl] Fixed tests failing on PHP 5.5 and removed this version from the allowed failures

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

Commits
-------

69ec7c8 Removed PHP 5.5 from the allowed failures.
3492186 [Intl] Fixed tests failing on PHP 5.5