Fix cat allocation YAML test (elastic#126003) (elastic#126029)

This test failed when the `disk.indices.forecast` value was a decimal number.
We adjust the regex to allow decimal values and for consistency we also allow negative values.

Fixes elastic#125711
Fixes elastic#125848
Fixes elastic#125661

(cherry picked from commit 8028d5a)

# Conflicts:
#	muted-tests.yml

Author: nielsbauman

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/cat.allocation/10_basic.yml

@@ -295,7 +295,7 @@
           ( [-\w.]+                \s+
             [-\w.]+                \s+
             [-\w.]+                \s+
-            [\w]+
+            [-\w.]+
             \n
           )+
         $/