ci: Enumerate all maintained branches in the GitHub Actions triggers

.github/workflows/lint.yml

diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 7a13d35..eb4734d 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -7,10 +7,12 @@
   push:
     branches:
       - libpng16
+      - libpng18
       - develop
   pull_request:
     branches:
       - libpng16
+      - libpng18
       - develop
 
 permissions:

.github/workflows/verify-linux.yml

diff --git a/.github/workflows/verify-linux.yml b/.github/workflows/verify-linux.yml
index e32bfc8..9e25d5f 100644
--- a/.github/workflows/verify-linux.yml
+++ b/.github/workflows/verify-linux.yml
@@ -8,10 +8,12 @@
     branches:
       - libpng16
       - libpng18
+      - develop
   pull_request:
     branches:
       - libpng16
       - libpng18
+      - develop
 
 permissions:
   contents: read

.github/workflows/verify-macos.yml

diff --git a/.github/workflows/verify-macos.yml b/.github/workflows/verify-macos.yml
index 50df104..be7ca52 100644
--- a/.github/workflows/verify-macos.yml
+++ b/.github/workflows/verify-macos.yml
@@ -8,10 +8,12 @@
     branches:
       - libpng16
       - libpng18
+      - develop
   pull_request:
     branches:
       - libpng16
       - libpng18
+      - develop
 
 permissions:
   contents: read

.github/workflows/verify-windows.yml

diff --git a/.github/workflows/verify-windows.yml b/.github/workflows/verify-windows.yml
index 43b67db..c45c6a8 100644
--- a/.github/workflows/verify-windows.yml
+++ b/.github/workflows/verify-windows.yml
@@ -8,10 +8,12 @@
     branches:
       - libpng16
       - libpng18
+      - develop
   pull_request:
     branches:
       - libpng16
       - libpng18
+      - develop
 
 permissions:
   contents: read