gha: fix workflow by allowing the composer-normalize plugin (#1412)

* gha: fix workflow by allowing the composer-normalize plugin

We don't need to enable it in the project itself, but at least in this
workflow which explicitly uses it.

See https://github.com/barryvdh/laravel-ide-helper/actions/runs/3980013548/jobs/6822812621#step:4:34
```
Error: ergebnis/composer-normalize (installed globally) contains a Composer plugin which is blocked by your allow-plugins config. You may add it to the list if you consider it safe.
You can run "composer global config --no-plugins allow-plugins.ergebnis/composer-normalize [true|false]" to enable it (true) or disable it explicitly and suppress this exception (false)
```

* gha: also run this workflow when it is changed itself

Author: mfn

.github/workflows/composer-normalize.yml

@@ -3,6 +3,7 @@ name: normalize composer.json
 on:
   push:
     paths:
+      - .github/workflows/composer-normalize.yml
       - composer.json
 
 jobs:
@@ -18,6 +19,7 @@ jobs:
 
       - name: Normalize composer.json
         run: |
+          composer global config --no-plugins allow-plugins.ergebnis/composer-normalize true
           composer global require ergebnis/composer-normalize
           composer normalize