uring <= 0.6 tests are not compatible with ocaml 5.1

```
\# /usr/bin/git --no-pager diff --no-index --color=always -u _build/default/README.md _build/default/.mdx/README.md.corrected
\# diff --git a/_build/default/README.md b/_build/default/.mdx/README.md.corrected
\# index 0bb1311..2888173 100644
\# --- a/_build/default/README.md
\# +++ b/_build/default/.mdx/README.md.corrected
\# @@ -39,7 +39,7 @@ To start, we'll open a file using `Uring.openat2`, which works much like the reg
\#        ~resolve:Uring.Resolve.beneath
\#        "test.log"
\#        `Open_log;;
\# -val open_file : _[> `Open_log ] Uring.job option = Some <abstr>
\# +val open_file : ([> `Open_log ] as '_weak2) Uring.job option = Some <abstr>
\#  ```
\#
\#  `submit` returns `None` if the submission queue is full.
\# @@ -117,13 +117,15 @@ Finally, we close the file:
\#
\#  ```ocaml
\#  # Uring.close uring fd `Close_log;;
\# -- : _[> `Close_log | `Open_log | `Write_all ] Uring.job option = Some <abstr>
\# +- : ([> `Close_log | `Open_log | `Write_all ] as '_weak3) Uring.job option =
\# +Some <abstr>
\#
\#  # Uring.submit uring;;
\#  - : int = 1
\#
\#  # wait_with_retry uring;;
\# -- : int * _[> `Close_log | `Open_log | `Write_all ] = (0, `Close_log)
\# +- : int * ([> `Close_log | `Open_log | `Write_all ] as '_weak3) =
\# +(0, `Close_log)
[...]
```

Signed-off-by: Marcello Seri <[email protected]>

Author: mseri

packages/uring/uring.0.4/opam

@@ -31,7 +31,7 @@ build: [
     "-j"
     jobs
     "@install"
-    "@runtest" {with-test}
+    "@runtest" {with-test & ocaml:version < "5.1"}
     "@doc" {with-doc}
   ]
 ]

packages/uring/uring.0.5/opam

@@ -31,7 +31,7 @@ build: [
     "-j"
     jobs
     "@install"
-    "@runtest" {with-test}
+    "@runtest" {with-test & ocaml:version < "5.1"}
     "@doc" {with-doc}
   ]
 ]

packages/uring/uring.0.6/opam

@@ -31,7 +31,7 @@ build: [
     "-j"
     jobs
     "@install"
-    "@runtest" {with-test}
+    "@runtest" {with-test & ocaml:version < "5.1.0"}
     "@doc" {with-doc}
   ]
 ]