Fix push -> pull_request event triggers

I originally tested in my fork where everything happened to be a push to a branch in the same repo.

.github/workflows/docker.yml

 name: Build Docker Images
 
 on:
+  pull_request:
+    paths-ignore:
+      - "*.md"
+      - "binder/**"
+      - "docs/**"
+      - "examples/**"
   push:
+    branches:
+      - master
     paths-ignore:
       - "*.md"
       - "binder/**"

.github/workflows/sphinx.yml

 name: Build Sphinx Documentation
 
 on:
+  pull_request:
+    paths:
+      - "docs/**"
+      - ".github/workflows/sphinx.yml"
   push:
+    branches:
+      - master
     paths:
       - "docs/**"
       - ".github/workflows/sphinx.yml"