build: change the fallback version suffix to `+git.{sha}`

Seems to be more commonly used than the current `-commit-{sha}`.
Also cleanup/simplify the version handling code.

Change-Id: I551c78632037c7156319b7ff7a327980f73ce265
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ed54263..5ef1f7b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,9 +2,13 @@
 on:
   push:
     paths-ignore:
+      - 'Dockerfile'
+      - '.dockerignore'
+      - '.editorconfig'
+      - '.gitignore'
+      - '.mailmap'
       - 'manpages/**'
       - '*.md'
-      - '.mailmap'
   workflow_dispatch:
 
 permissions: {}