chore(test-pr.sh): commit merge as `qTox testing <>`

With this one doesn't need to even have git properly configured to test
a PR.

merge-pr.sh

@@ -55,7 +55,7 @@ main() {
     add_remote
     get_sources
 
-    merge "-S" \
+    merge git merge -S \
         && after_merge_msg $merge_branch \
         || after_merge_failure_msg $merge_branch
 }

test-pr.sh

@@ -54,7 +54,8 @@ main() {
     add_remote "https"
     get_sources
 
-    merge "--no-gpg-sign" \
+    merge git -c user.email='<>' -c user.name='qTox testing' \
+        merge --no-gpg-sign \
             && after_merge_msg $merge_branch \
             || after_merge_failure_msg $merge_branch
 }

tools/lib/PR_bash.source

@@ -104,8 +104,7 @@ get_sources() {
 
 # check whether to sign
 merge() {
-    local signed="$@"
-    git merge --no-ff $signed $PR -m "Merge pull request #$PR
+    "${@}" --no-ff $PR -m "Merge pull request #$PR
 $OPT_MSG
 $(git shortlog master..$PR)"
 }