Allow for running various workflows via workflow dispatch

It seems we forgot to do this, but it's useful e.g. to run the test workflow manually.

Author: alexdewar

.github/workflows/cargo-test.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches: [main]
   pull_request:
+  workflow_dispatch:
 
 env:
   CARGO_TERM_COLOR: always

.github/workflows/check-docs.yml

@@ -3,6 +3,7 @@ on:
   push:
     branches: [main]
   pull_request:
+  workflow_dispatch:
   schedule:
     - cron: "0 0 * * 1" # midnight every Monday
 

.github/workflows/pre-commit.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches: [main]
   pull_request:
+  workflow_dispatch:
 
 jobs:
   pre-commit: