mailmap: associate dangling bot commit with github-actions[bot] account

* One github-actions[bot] commit had set the author differently to the
  others which caused the shortlog action to fail.

.mailmap

@@ -1,3 +1,5 @@
+Alex Reinecke              <[email protected]>
+Alex Reinecke              <[email protected]>      P. A. Reinecke      <[email protected]>
 Alexander Paulsell         <[email protected]> AlexanderPaulsell   <[email protected]>
 Ben Fitzpatrick            <[email protected]>   benfitzpatrick      <[email protected]>
 Bruno Kinoshita            <[email protected]>
@@ -16,7 +18,7 @@ Hilary Oliver              <[email protected]>
 Hilary Oliver              <[email protected]>
 Hilary Oliver              <[email protected]>
 Hilary Oliver              <[email protected]>
-Hilary Oliver             <[email protected]>
+Hilary Oliver              <[email protected]>
 Ivor Blockley              <[email protected]>           Ivor Blockley       <[email protected]>
 Jonathan Thomas            <[email protected]>         Jonathan Thomas     <[email protected]>
 Jonathan Thomas            <[email protected]>         Jonathan Thomas     <[email protected]>
@@ -35,8 +37,6 @@ Matt Shin                  <[email protected]>      matthewrmshin
 Matt Shin                  <[email protected]>      matthewrmshin       <[email protected]>
 Mel Hall                   <[email protected]>
 Oliver Sanders             <[email protected]>    Oliver sanders      <[email protected]>
-Alex Reinecke           <[email protected]>
-Alex Reinecke           <[email protected]>      P. A. Reinecke      <[email protected]>
 Prasanna Challuri          <[email protected]>       challurip           <[email protected]>
 Ronnie Dutta               <[email protected]>
 Rosalyn Hatcher            <[email protected]>          RosalynHatcher      <[email protected]>
@@ -50,3 +50,4 @@ Tim Whitcomb               <[email protected]>       Tim Whitcomb
 Tim Whitcomb               <[email protected]>       trwhitcomb          <[email protected]>
 Tomek Trzeciak             <[email protected]>   Tomek Trzeciak      <[email protected]>
 Tomek Trzeciak             <[email protected]>   TomekTrzeciak       <[email protected]>
+github-actions[bot]        <41898282+github-actions[bot]@users.noreply.github.com>

CONTRIBUTING.md

@@ -22,7 +22,7 @@ Issue](https://github.com/cylc/cylc-flow/issues) as the team may not be able to
 consider large changes that appear out of the blue. New contributors should
 add their details to the [Code Contributors](#code-contributors) section of
 this file as part of their first Pull Request, and reviewers are responsible
-for checking this before merging the new branch into *master*.
+for checking this before merging the new branch.
 
 ## Code Contributors