I'm missing something simple and essential in promtail

With a very simple config

scrape_configs:
- job_name: int3
  static_configs:
    - targets:
        - localhost
      labels:
        job: int3
        __path__: /usr/local/stack/db/logs/*.log
  pipeline_stages:
    - regex:
        expression: "BEGIN failed"
    - labels:
        level: error

and simple logs

Can't locate nonexistent.pm in @INC (you may need to install the nonexistent module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.28.1 /usr/local/share/perl/5.28.1 /usr/lib/x86_64-linux-gnu/perl5/5.28 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.28 /usr/share/perl/5.28 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /home/tarkhil/GIT/test line 3.
BEGIN failed--compilation aborted at /home/tarkhil/GIT/test line 3.

tail -2 /usr/local/stack/db/logs/test.log | promtail --stdin --dry-run --inspect -config.file /etc/promtail/pipeline.yaml

shows me

Clients configured:
----------------------
url: http://127.0.0.1:3100/loki/api/v1/push
batchwait: 1s
batchsize: 1048576
follow_redirects: false
backoff_config:
  min_period: 500ms
  max_period: 5m0s
  max_retries: 10
timeout: 10s
tenant_id: ""
stream_lag_labels: filename

[inspect: regex stage]: none
[inspect: regex stage]: none
[inspect: labels stage]: none
2022-07-17T13:06:32.878357+0300{__path__="/usr/local/stack/db/logs/*.log", job="int3"}Can't locate nonexistent.pm in @INC (you may need to install the nonexistent module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.28.1 /usr/local/share/perl/5.28.1 /usr/lib/x86_64-linux-gnu/perl5/5.28 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.28 /usr/share/perl/5.28 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /home/tarkhil/GIT/test line 3.
[inspect: labels stage]: none
2022-07-17T13:06:32.878358242+0300      {__path__="/usr/local/stack/db/logs/*.log", job="int3"}BEGIN failed--compilation aborted at /home/tarkhil/GIT/test line 3.
level=info ts=2022-07-17T10:06:32.879467249Z caller=server.go:260 http=[::]:9080 grpc=[::]:35423 msg="server listening on addresses"
level=info ts=2022-07-17T10:06:32.879627515Z caller=main.go:119 msg="Starting Promtail" version="(version=2.4.2, branch=HEAD, revision=525040a32)"

Why none? How do I do the simple task of marking some log lines as critical errors?