Remove branches part from merge_group GH actions configuration (#5308)

### Description
Remove branches part from merge_group GH actions configuration, in an
attempt to make the merge queue work

### How has this been tested?
Not, but I don't see a risk with trying this.

<small>By submitting this pull request, I confirm that my contribution
is made under the terms of the [MIT
license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).</small>

.github/workflows/doc-tests.yml

@@ -11,7 +11,6 @@ on:
  pull_request:
  branches: [ master, main-* ]
  merge_group:
- branches: [ master, main-* ]
 
 concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}

.github/workflows/msbuild.yml

@@ -5,7 +5,6 @@ on:
  pull_request:
  branches: [ master, main-* ]
  merge_group:
- branches: [ master, main-* ]
 
 concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}

.github/workflows/refman.yml

@@ -5,7 +5,6 @@ on:
  pull_request:
  branches: [ master, main-* ]
  merge_group:
- branches: [ master, main-* ]
 
 concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}

.github/workflows/runtime-tests.yml

@@ -5,7 +5,6 @@ on:
  pull_request:
  branches: [ master, main-* ]
  merge_group:
- branches: [ master, main-* ]
 
 concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}

.github/workflows/standard-libraries.yml

@@ -5,7 +5,6 @@ on:
  pull_request:
  branches: [ master, main-* ]
  merge_group:
- branches: [ master, main-* ]
 
 concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}