fix more comet versions in docs (#2374)

Author: andygrove

docs/source/user-guide/latest/datasources.md

@@ -94,7 +94,7 @@ root
  |    |-- lastName: string (nullable = true)
  |    |-- ageInYears: integer (nullable = true)
 
-25/01/30 16:50:43 INFO core/src/lib.rs: Comet native library version 0.9.0 initialized
+25/01/30 16:50:43 INFO core/src/lib.rs: Comet native library version $COMET_VERSION initialized
 == Physical Plan ==
 * CometColumnarToRow (2)
 +- CometNativeScan:  (1)

docs/source/user-guide/latest/source.md

@@ -27,7 +27,7 @@ Official source releases can be downloaded from https://dist.apache.org/repos/di
 
 ```console
 # Pick the latest version
-export COMET_VERSION=0.9.0
+export COMET_VERSION=$COMET_VERSION
 # Download the tarball
 curl -O "https://dist.apache.org/repos/dist/release/datafusion/datafusion-comet-$COMET_VERSION/apache-datafusion-comet-$COMET_VERSION.tar.gz"
 # Unpack