Fix merge queue CI (open-telemetry#11797)

#### Description

This PR removes the `merge_group` trigger from the two CI checks that
failed in merge queues (but not in PRs). See tracking issue for details.

The reasoning for simply disabling them instead of modifying them to
work in merge queues is three-fold:
- For `changelog` to be meaningful, it needs to only run for PRs with no
`[chore]` title tag or `Skip changelog` label, but it seems there is no
simple way to access this data in merge queue workflows unfortunately.
(A possible complicated way may be to parse the ref (PR branch) name and
query the title and labels in a script with the `gh` command.)
- `api-compatibility` is never meaningful because it seems to have been
broken for a long time (see open-telemetry#7443)
- Both `changelog` and `api-compatibility` are checks on the _set of
changes_ made by a PR, not on the resulting state of the codebase. As
such, their result should not meaningfully change when merged against an
old main vs. a newer main, making running them in the merge queue
pointless.

#### Link to tracking issue
Fixes open-telemetry#11790

This should let us try [enabling the merge
queue](open-telemetry/community#2469) again.

#### Testing
Testing merge queue checks is unfortunately quite difficult, but since
we're only disabling checks I don't foresee any issues.

.github/workflows/api-compatibility.yml

@@ -9,8 +9,6 @@ on:
   pull_request:
     branches:
       - main
-  merge_group:
-    types: [checks_requested]
 
 permissions:
   contents: read

.github/workflows/changelog.yml

@@ -9,8 +9,6 @@ on:
     types: [opened, ready_for_review, synchronize, reopened, labeled, unlabeled]
     branches:
       - main
-  merge_group:
-    types: [checks_requested]
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref }}