Add coverage baseline commit to git-blame-ignore (#1613)

Author: maxisbey

.git-blame-ignore-revs

@@ -1,2 +1,5 @@
 # Applied 120 line-length rule to all files: https://github.com/modelcontextprotocol/python-sdk/pull/856
 543961968c0634e93d919d509cce23a1d6a56c21
+
+# Added 100% code coverage baseline with pragma comments: https://github.com/modelcontextprotocol/python-sdk/pull/1553
+89e9c43acf7e23cf766357d776ec1ce63ac2c58e