Enable testing of merge-queues

From [1]

[1]: https://review.trustedfirmware.org/c/next/ci/mbed-tls-job-configs/+/22109

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: Iae654e6967ab06f1c8a76786962e180bcf54b74f
diff --git a/mbed-tls-pr-merge.yaml b/mbed-tls-pr-merge.yaml
index 1441477..521ab92 100644
--- a/mbed-tls-pr-merge.yaml
+++ b/mbed-tls-pr-merge.yaml
@@ -38,7 +38,7 @@
         discover-pr-forks-strategy: both
         discover-pr-forks-trust: permission
         discover-pr-origin: both
-        head-filter-regex: '(?!^PR-(1824)-(merge|head)$)(PR-\d+-merge)'
+        head-filter-regex: '(?!^PR-(7958|7959)-(merge|head)$)(PR-\d+-merge)'
         property-strategies:
           all-branches:
           - pipeline-branch-durability-override: performance-optimized