[ci] Disable download tests unless specifically invoked

Tests can be enabled/disabled using the following in the commit message
* Run Download: `ci-run-dl`
* Skip Core: `ci-skip`
* Skip Quick & Core: `ci-skip-all`
(replace "-" by a space " ")

.github/workflows/core.yml

@@ -3,7 +3,7 @@ on: [push, pull_request]
 jobs:
   tests:
     name: Core Tests
-    if: "!contains(github.event.head_commit.message, 'ci skip all')"
+    if: "!contains(github.event.head_commit.message, 'ci skip')"
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: true

.github/workflows/download.yml

@@ -3,7 +3,7 @@ on: [push, pull_request]
 jobs:
   tests:
     name: Download Tests
-    if: "!contains(github.event.head_commit.message, 'ci skip dl') && !contains(github.event.head_commit.message, 'ci skip all')"
+    if: "contains(github.event.head_commit.message, 'ci run dl')"
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: true