Update build workflow

Currently the branch protection is set on specific workflows which needs
to be run every time a PR is created (or a push).

Because it isn't possible to tell the branch protection only to do it's
job if specific files are touched or not, we just need to make sure
these jobs are always started.

Also, because we now check the builds for an MSRV, and the title would
change all the time, that would cause the branch protection to be
updated everytime the MSRV would change. This is now also addressed by
naming that job 'msrv' instead of the version number.

.github/workflows/hadolint.yml

@@ -1,13 +1,9 @@
 name: Hadolint
 
-on:
-  push:
-    paths:
-      - "docker/**"
-
-  pull_request:
-    paths:
-      - "docker/**"
+on: [
+      push,
+      pull_request
+    ]
 
 jobs:
   hadolint: