ci: disable stale testbench failure reporting

Why: The historic testbench failure-reporting backend no longer exists, so CI jobs should stop trying to post failures there.

Impact: CI failures no longer attempt outbound reports to the removed backend.

Before/After: CI exported RSYSLOG_STATSURL to a dead endpoint; CI now leaves it unset and diag.sh uses its local no-report path.

Technical Overview: Removed RSYSLOG_STATSURL from the regular container CI job, Elasticsearch matrix, Kafka distcheck lane, distro daily matrix, and impstats push workflow. The diag.sh helper remains unchanged so explicit local or future CI opt-ins can still provide a replacement URL. The devcontainer pass-through remains intact for manual users that intentionally set RSYSLOG_STATSURL.

With the help of AI-Agents: Codex

.github/workflows/impstats_push_victoriametrics.yml

@@ -81,8 +81,6 @@ jobs:
           CI_CHECK_CMD: check
           ABORT_ALL_ON_TEST_FAIL: 'NO'
           CI_VALGRIND_SUPPRESSIONS: ubuntu22.04.supp
-          RSYSLOG_STATSURL: >-
-            http://build.rsyslog.com/testbench-failedtest.php
           USE_AUTO_DEBUG: 'off'
           VERBOSE: '1'
         run: |

.github/workflows/run_checks.yml

@@ -501,7 +501,6 @@ jobs:
           CODECOV_commit_sha="$(git rev-parse HEAD)"
           export CODECOV_commit_sha
           export RSYSLOG_CONTAINER_UID="" # use default
-          export RSYSLOG_STATSURL='http://build.rsyslog.com/testbench-failedtest.php'
           export CFLAGS='-g'
           export CC='gcc'
           export CI_CONFIGURE_CACHE=1
@@ -1249,7 +1248,6 @@ jobs:
           CI_CHECK_CMD: check
           ABORT_ALL_ON_TEST_FAIL: 'NO'
           CI_VALGRIND_SUPPRESSIONS: ubuntu22.04.supp
-          RSYSLOG_STATSURL: http://build.rsyslog.com/testbench-failedtest.php
           CI_CONFIGURE_CACHE: '1'
           USE_AUTO_DEBUG: 'off'
           VERBOSE: '1'
@@ -1464,7 +1462,6 @@ jobs:
                  --disable-default-tests \
                  --enable-omkafka --enable-gnutls --disable-gnutls-tests --enable-imkafka"
           export RSYSLOG_CONTAINER_UID="" # use default
-          export RSYSLOG_STATSURL='http://build.rsyslog.com/testbench-failedtest.php'
           export CC='gcc'
           export CFLAGS='-g'
           export CI_CONFIGURE_CACHE=1

.github/workflows/run_distro_daily.yml

@@ -94,7 +94,6 @@ jobs:
           export CODECOV_repo_slug=''
           export CODECOV_commit_sha=''
           export RSYSLOG_CONTAINER_UID=''
-          export RSYSLOG_STATSURL='http://build.rsyslog.com/testbench-failedtest.php'
           export CFLAGS='-g'
           export CC='gcc'
           export CI_CONFIGURE_CACHE=1