dependabot: drop open-pull-request-limit

Currently, dependabot is for some reason stuck saying  "Dependabot
cannot open any more pull requests" (the error message one gets if there
are many than open-pull-request-limit dependabot PRs open), despite
there being exactly 0 open dependabot PRs. We also cannot manually
trigger it, as it fails with the same reason.

Try to resolve this by removing the limit on pull requests. In practice,
this should not matter, as we have exactly 1 submodule, and the cargo
dependencies are all grouped, meaning simply based on how dependabot
functions, we never get more than one concurrent PR of each type anyway.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

.github/dependabot.yml

@@ -6,15 +6,13 @@ updates:
   directory: "/"
   schedule:
     interval: monthly
-  open-pull-requests-limit: 1
 
 # A monthly update to rust dependencies. These will be grouped,
 # e.g. one PR will contains updates for all dependencies.
 - package-ecosystem: cargo
   directory: "/"
   schedule:
     interval: monthly
-  open-pull-requests-limit: 1
   # Make it also update transitive dependencies in Cargo.lock
   allow:
     - dependency-type: "all"