Don't warn about a mid-page instrumental more than once

__main__.py

@@ -1247,7 +1247,7 @@ def _calculate_instrumental_time(
             > last_syllable_page
         )
         # If this syllable is not the last one in this page
-        if not syllable_is_last_in_page:
+        if not instrumental._warned and not syllable_is_last_in_page:
             # Warn the user
             logger.warning(
                 "instrumentals should not be triggered in the middle "
@@ -1267,6 +1267,7 @@ def _calculate_instrumental_time(
                     for li in range(lyric.lines_per_page)
                 )
             )
+            instrumental._warned = True
 
         # If this line is being actively sung, and this is the last
         # syllable in this line

config.py

@@ -72,6 +72,9 @@ class SettingsInstrumental:
     transition: str | None = None
     x: int = 0
     y: int = 0
+    # HACK This property exists to ensure that only one warning is
+    # logged for starting an instrumental in the middle of a page.
+    _warned: bool = False
 
 
 @define