Don't limit number of open Dependabot pull requests

The Dependabot service is used to keep the project dependencies updated.

Thanks to the project's high quality validation infrastructure, the human effort required to complete a trivial version
bump is minimal. However, some bumps may introduce breaking changes that would require a significant amount of effort to
accommodate, or are blocked by external tasks. In this case, the Dependabot pull request can't be merged, but should be
left open to track the need to perform the bump when it is feasible. This means that it should be expected that there
will be regularly be a small number of Dependabot pull requests left open in the repository over long periods of time.
The automated system is here to assist the human project maintainers, not as a tyrannical overlord, so this is the
system working exactly as intended.

By default, Dependabot is configured to stop submitting pull requests if it already has five open pull requests. This
means that if it happens that the accumulation of intentionally on-hold pull requests reaches that number, the project
stops receiving the easily handled trivial update PRs. This is very harmful because it results in the completely
unnecessary use of outdated dependencies, and unnecessary challenging large bumps when pull requests start being
submitted once more after the backlog is cleared.

The harmful default configuration is hereby overridden by configuring the maximum open pull request limit at 100. This
value was chosen as an arbitrary large number simply to functionally disable the limiting, rather than from any
expectation that the actual number of open PRs can ever reach that count.

Author: per1234

.github/dependabot.yml

@@ -7,6 +7,7 @@ updates:
   # See: https://docs.github.com/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot
   - package-ecosystem: github-actions
     directory: /.github/workflows/
+    open-pull-requests-limit: 100
     schedule:
       interval: daily
     labels:
@@ -17,6 +18,7 @@ updates:
   # Configure check for outdated GitHub Actions actions in workflow templates.
   - package-ecosystem: github-actions
     directory: /workflow-templates/
+    open-pull-requests-limit: 100
     schedule:
       interval: daily
     labels:
@@ -26,6 +28,7 @@ updates:
 
   - package-ecosystem: npm
     directory: /
+    open-pull-requests-limit: 100
     schedule:
       interval: daily
     labels:
@@ -35,6 +38,7 @@ updates:
 
   - package-ecosystem: pip
     directory: /
+    open-pull-requests-limit: 100
     schedule:
       interval: daily
     labels: