Add picosvg to optimization step (#883)

* Add picosvg to optimization step

This should help remove `fill-rule="evenodd"` from SVGs, improving where
they can be rendered.

* Create thick-lions-explain.md

Author: eliperkins

.changeset/thick-lions-explain.md

@@ -0,0 +1,5 @@
+---
+"@primer/octicons": patch
+---
+
+Remove fill-rule from SVGs using picosvg as an optimization step

.github/actions/python/requirements.txt

@@ -0,0 +1 @@
+picosvg~=0.20.6

.github/workflows/optimize.yml

@@ -1,19 +1,34 @@
 on: 
   push:
     paths:
-    - 'icons/**'
-    - '.github/workflows/optimize.yml'
+      - 'icons/**'
+      - '.github/workflows/optimize.yml'
+      - '.github/actions/python/requirements.txt'
+  pull_request:
+    paths:
+      - 'icons/**'
+      - '.github/workflows/optimize.yml'
+      - '.github/actions/python/requirements.txt'
 name: Optimize SVGs
 jobs:
   optimize:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@master
+
+      - uses: actions/setup-python@v4
+        with:
+          python-version: '3.10' 
+          cache: 'pip'
+      - run: pip install -r .github/actions/python/requirements.txt
+      - run: for icon in icons/*; do picosvg $icon --output_file $icon; done
+
       - uses: actions/setup-node@master
         with:
           node-version: '10.x'
       - run: npm install
       - run: npm run svgo
+
       - uses: EndBug/add-and-commit@v4
         with:
           add: 'icons'