Set redirects update branch to test branch

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>

.readthedocs.yaml

@@ -17,7 +17,7 @@ build:
     post_build:
     - |
       # Work around Readthedocs bug: Command parsing fails if the 'if' statement is on the first line
-      if [ "$READTHEDOCS_VERSION" = "development" ]; then
+      if [ "$READTHEDOCS_VERSION" = "dev-bensze01-in-tree-redirects-test" ]; then
         "$READTHEDOCS_VIRTUALENV_PATH/bin/rtd" projects "Mbed TLS API" redirects sync --wet-run -f docs/redirects.yaml
       fi