minor #14644 [Lock] - replace getExpiringDate by getRemainingLifetime (ybenhssaien)

This PR was submitted for the 5.2 branch but it was merged into the 4.4 branch instead.

Discussion
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[Lock] - replace getExpiringDate by getRemainingLifetime

As the method `getExpiringDate` doesn't exist, replace it by `getRemainingLifetime` which returns the remaining time to live in seconds

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Commits
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f812114 Lock - replace getExpiringDate by getRemainingLifetime

Author: javiereguiluz

components/lock.rst

@@ -196,8 +196,8 @@ to reset the TTL to its original value::
         $lock->refresh(600);
 
 This component also provides two useful methods related to expiring locks:
-``getExpiringDate()`` (which returns ``null`` or a ``\DateTimeImmutable``
-object) and ``isExpired()`` (which returns a boolean).
+``getRemainingLifetime()`` (which returns ``null`` or a ``float``
+as seconds) and ``isExpired()`` (which returns a boolean).
 
 The Owner of The Lock
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