ci: set a common B2C_JOB_SUCCESS_REGEX with the message that's printed for all jobs

Simpler code, and more reliable against serial corruption because that
message is printed 4 times (vs only once for the other ones).

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29608>

.gitlab-ci/test/gitlab-ci.yml

@@ -131,7 +131,6 @@ python-test:
       - results/vkd3d-proton.log
   variables:
     HWCI_TEST_SCRIPT: ./install/vkd3d-proton/run.sh
-    B2C_JOB_SUCCESS_REGEX: 'vkd3d-proton execution: SUCCESS\r$'
 
 .piglit-traces-test:
   artifacts:
@@ -287,7 +286,7 @@ python-test:
     # boot2container initrd configuration parameters.
     B2C_KERNEL_URL: 'https://gitlab.freedesktop.org/gfx-ci/ci-tron/-/package_files/519/download'  # Linux 6.1
     B2C_INITRAMFS_URL: 'https://gitlab.freedesktop.org/mupuf/boot2container/-/releases/v0.9.10/downloads/initramfs.linux_amd64.cpio.xz'
-    B2C_JOB_SUCCESS_REGEX: '\[.*\]: Execution is over, pipeline status: 0\r$'
+    B2C_JOB_SUCCESS_REGEX: 'hwci: mesa: pass\r$'
     B2C_LOG_LEVEL: 6
     B2C_POWEROFF_DELAY: 15
     B2C_SESSION_END_REGEX: '^.*It''s now safe to turn off your computer\r$'