CI: Run some checks on push on 1.3.x (pandas-dev#42538)

Author: lithomas1

.github/workflows/posix.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - master
+      - 1.3.x
   pull_request:
     branches:
       - master

.github/workflows/pre-commit.yml

@@ -5,6 +5,7 @@ on:
   push:
     branches:
       - master
+      - 1.3.x
 
 jobs:
   pre-commit:

.github/workflows/sdist.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - master
+      - 1.3.x
   pull_request:
     branches:
       - master