diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 6767cd306f7..f0816af5f7d 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -1,7 +1,7 @@
 # Try to get a short workflow name and a job name that start with Python
 # version to make it easier to check the status inside GitHub UI.
 #
-# When using external actions check that the extenral repos are permitted via
+# When using external actions check that the external repos are permitted via
 # the GitHub configuration at https://github.com/twisted/twisted/settings/actions
 #
 name: CI
@@ -14,6 +14,13 @@ on:
   pull_request:
     branches: [ trunk ]
 
+  workflow_dispatch:
+    inputs:
+      debug_enabled:
+        type: boolean
+        description: 'Run the build with tmate debugging enabled (https://github.com/marketplace/actions/debugging-with-tmate)'
+        required: false
+        default: false
 
 # Only have a run a single parallel for each branch.
 # Runs for trunk are queues.
@@ -30,27 +37,26 @@ defaults:
 
 env:
   # Set to 'yes' to open a tunnel to GitHub's VMs through tmate on failures.
+  # You can also trigger it via manual workflow trigger.
+  # https://github.com/mxschmitt/action-tmate#manually-triggered-debug
   TMATE_DEBUG: 'no'
   # The default values in the job generated by the matrix.
-  DEFAULT_JOB_NAME: 'lnx-default-tests'
   DEFAULT_PYTHON_VERSION: '3.10'
-  DEFAULT_RUNS_ON: 'ubuntu-20.04'
-  DEFAULT_TOX_ENV: 'alldeps-withcov-posix'
-  DEFAULT_TRIAL_ARGS: '-j 4'
 
 jobs:
   testing:
-    name: ${{ matrix.python-version || env.DEFAULT_PYTHON_VERSION }}-${{ matrix.job-name || env.DEFAULT_JOB_NAME }}
+    # We can't use `env.*` in the job name, only in the steps.
+    name: ${{ matrix.python-version }}-${{ matrix.job-name || 'default-tests' }}
     # We have Ubuntu as the base for running agains multiple Python versions.
-    runs-on: "${{ matrix.runs-on || env.DEFAULT_RUNS_ON }}"
+    runs-on: "${{ matrix.runs-on || 'ubuntu-20.04' }}"
     env:
       # By default we run all tests with all deps with coverage.
-      TOXENV: "${{ matrix.tox-env || env.DEFAULT_TOX_ENV }}"
+      TOXENV: "${{ matrix.tox-env || 'alldeps-withcov-posix' }}"
       # As of April 2021 GHA VM have 2 CPUs - Azure Standard_DS2_v2
       # Trial distributed jobs enabled to speed up the CI jobs.
       # On Windows, we don't yet enable distributed tests as is not yet
       # supported.
-      TRIAL_ARGS: "${{ matrix.trial-args || env.DEFAULT_TRIAL_ARGS }}"
+      TRIAL_ARGS: "${{ matrix.trial-args || '-j 4' }}"
     strategy:
       fail-fast: false
       # The matrix is designed to not expand into any job.
@@ -77,7 +83,7 @@ jobs:
         tox-wrapper: ['']
         # Tests are executed with the default target which is the full test suite.
         trial-target: ['']
-        # By default the coverate is not skipped.
+        # By default the coverage is not skipped.
         skip-coverage: ['']
 
         # Here the matrix is extended with variations of the default
@@ -138,14 +144,14 @@ jobs:
           # gain from reporting coverage.
           - python-version: pypy-3.7
             tox-env: alldeps-nocov-posix
-            job-name: 'pypy-no-coverage'
+            job-name: 'no-coverage'
             skip-coverage: yes
 
           # We still run some tests with coverage,
           # as there are test with specific code branches for pypy.
           - python-version: pypy-3.7
             trial-target: twisted.test.test_compat twisted.test.test_defer twisted.internet.test.test_socket twisted.trial.test.test_tests
-            job-name: 'pypy-coverage'
+            job-name: 'with-coverage'
 
           # We run selected test for GTK reactor inside X virtual framebuffer.
           - python-version: '3.7'
@@ -215,8 +221,9 @@ jobs:
         ${{ matrix.tox-wrapper }} tox ${{ matrix.trial-target }}
 
     # If one of the above steps fails, fire up tmate for remote debugging.
-    - name: Tmate debug on failure
-      if: ${{ !cancelled() && env.TMATE_DEBUG == 'yes' }}
+    # This is fired for manual trigger or via the environment variable.
+    - name: Tmate debug session
+      if: ${{ !cancelled() && (env.TMATE_DEBUG == 'yes' || github.event_name == 'workflow_dispatch' && inputs.debug_enabled ) }}
       uses: mxschmitt/action-tmate@v3
       with:
         limit-access-to-actor: true