Set treosh/lighthouse-ci-action to 12.1.0 (#2223)

In the past couple of the weeks the performance score for the Lighthouse
audit dropped below 0.8 and started making CI fail.

This change in the CI result was surprising because there have been very
few commits to main since 3e74810, and
none that should have affected the Lighthouse performance score.

Looking for a culprit, I noticed that the `v12` tag for
`treosh/lighthouse-ci-action` was updated 2 weeks ago, pointing the tag
from Lighthouse version 12.1.0 to 12.6.0, which one can see in the
[treosh/lighthouse-ci-action
releases](https://github.com/treosh/lighthouse-ci-action/tags). There
are a good number of changes between those two versions, as shown in the
[Lighthouse
releases].(https://github.com/GoogleChrome/lighthouse/releases), but I
haven't yet identified which of them may have affected the score.

But before investigating too deeply, the easiest thing we can do to test
this hypothesis is to downgrade the version of the GitHub action, and
see if that fixes CI.

---------

Co-authored-by: Tania Allard <[email protected]>

Author: gabalafou

.github/workflows/docs.yml

@@ -110,7 +110,8 @@ jobs:
           DOCS_DIR: "audit"
 
       - name: "Audit with Lighthouse 🔦"
-        uses: treosh/lighthouse-ci-action@v12
+        # pin to Lighthouse version 12.1.0
+        uses: treosh/lighthouse-ci-action@2f8dda6cf4de7d73b29853c3f29e73a01e297bd8
         with:
           configPath: ".github/workflows/lighthouserc.json"
           temporaryPublicStorage: true