Dependabot: monthly grouped PR if there are Github Actions updates (#3565)

## Description:

To save on manual work, have Dependabot check monthly and create a
grouped PR for Github Actions updates. Hat tip @deshack for the tip and
grouping suggestion.

- For example we can update `actions/checkout@v5` to
`actions/checkout@v6` already and now Dependabot will propose to do that
for us. The first PR for this and other updates can be expected once
this PR has been merged.

-
https://docs.github.com/en/code-security/how-tos/secure-your-supply-chain/secure-your-dependencies/keeping-your-actions-up-to-date-with-dependabot
- Added brackets round the wildcard for patterns, as a bugfix for
reports such as these:
https://github.com/dependabot/dependabot-core/issues/13919. Bugfix comes
from:
https://discord.com/channels/1359946986937258015/1483653625342464071/1489364119009366240

- (To be clear, this does NOT add creating Version updates PRs for
dependencies, that is other functionality that works differently and we
don't have it enabled:
https://docs.github.com/en/code-security/how-tos/secure-your-supply-chain/secure-your-dependencies/configuring-dependabot-version-updates.
It also does not touch our currently enabled Security updates.)

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

tryout33

.github/dependabot.yml

@@ -0,0 +1,15 @@
+# Update schedule for GitHub Actions https://docs.github.com/en/code-security/how-tos/secure-your-supply-chain/secure-your-dependencies/keeping-your-actions-up-to-date-with-dependabot
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    groups:
+      updates:
+        applies-to: version-updates
+        patterns: ["*"] #wildcard, needs brackets as bugfix apparently
+      security:
+        applies-to: security-updates
+        patterns: ["*"]