Run only a single job per workflow matrix at a time

This limits each run of these workflows to a single
active matrix job. This means, for each PR, merge or
release only five jobs run concurrently.

.github/workflows/deb.yml

@@ -17,6 +17,7 @@ jobs:
 
     strategy:
       fail-fast: false
+      max-parallel: 1
       matrix:
         distro:
           - name: debian

.github/workflows/raspbian.yml

@@ -17,6 +17,7 @@ jobs:
 
     strategy:
       fail-fast: false
+      max-parallel: 1
       matrix:
         codename:
           - bullseye

.github/workflows/rpm.yml

@@ -17,6 +17,7 @@ jobs:
 
     strategy:
       fail-fast: false
+      max-parallel: 1
       matrix:
         distro:
           - name: rhel

.github/workflows/windows.yml

@@ -17,6 +17,7 @@ jobs:
 
     strategy:
       fail-fast: false
+      max-parallel: 1
       matrix:
         bits: [32, 64]