.github/workflows: run tests on the right branch

I copy/paste-d from another repo earlier and didn't realize
this repo uses 'master' as its main branch.

Signed-off-by: Brad Fitzpatrick <brad@danga.com>

.github/workflows/tests-lint.yaml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-      - "main"
+      - "master"
   pull_request:
     # all PRs on all branches
 name: "tests/lint"

.github/workflows/tests-linux.yml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-      - "main"
+      - "master"
   pull_request:
     # all PRs on all branches
 name: "tests/linux"

.github/workflows/tests-macos.yml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-      - "main"
+      - "master"
   pull_request:
     # all PRs on all branches
 name: "tests/macos"

.github/workflows/tests-tidy.yaml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-      - "main"
+      - "master"
   pull_request:
     # all PRs on all branches
 name: "tests/tidy"

.github/workflows/tests-windows.yml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-      - "main"
+      - "master"
   pull_request:
     # all PRs on all branches
 name: "tests/windows"