[Test] Fix reference/cat/allocation/line_8 test failure

In this test, 260b is replaced by the regexp \d+b
but the test sometimes produces results like 1.1kb
so this commit adapts the regexp to match values
with decimals

closes #26685

Author: tlrx

docs/reference/cat/allocation.asciidoc

@@ -18,7 +18,7 @@ Might respond with:
 shards disk.indices disk.used disk.avail disk.total disk.percent host      ip        node
      5         260b    47.3gb     43.4gb    100.7gb           46 127.0.0.1 127.0.0.1 CSUXak2
 --------------------------------------------------
-// TESTRESPONSE[s/260b/\\d+b/ s/\d+(\.\d+)?[tgmk]?b/\\d+(\\.\\d+)?[tgmk]?b/ s/46/\\d+/]
+// TESTRESPONSE[s/\d+(\.\d+)?[tgmk]?b/\\d+(\\.\\d+)?[tgmk]?b/ s/46/\\d+/]
 // TESTRESPONSE[s/CSUXak2/.+/ _cat]
 
 Here we can see that each node has been allocated a single shard and