[RELEASE] Released version 2.3-dev9

Released version 2.3-dev9 with the following main changes :
    - CLEANUP: http_ana: remove unused assignation of `att_beg`
    - BUG/MEDIUM: ssl: OCSP must work with BoringSSL
    - BUG/MINOR: log: fix memory leak on logsrv parse error
    - BUG/MINOR: log: fix risk of null deref on error path
    - BUILD: ssl: more elegant OpenSSL early data support check
    - CI: github actions: update h2spec to 2.6.0
    - BUG/MINOR: cache: Check the return value of http_replace_res_status
    - MINOR: cache: Store the "Last-Modified" date in the cache_entry
    - MINOR: cache: Process the If-Modified-Since header in conditional requests
    - MINOR: cache: Create res.cache_hit and res.cache_name sample fetches
    - MINOR: mux-h2: register a stats module
    - MINOR: mux-h2: add counters instance to h2c
    - MINOR: mux-h2: add stats for received frame types
    - MINOR: mux-h2: report detected error on stats
    - MINOR: mux-h2: count open connections/streams on stats
    - BUG/MINOR: server: fix srv downtime calcul on starting
    - BUG/MINOR: server: fix down_time report for stats
    - BUG/MINOR: lua: initialize sample before using it
    - MINOR: cache: Add Expires header value parsing
    - MINOR: ist: Add a case insensitive istmatch function
    - BUG/MINOR: cache: Manage multiple values in cache-control header value
    - BUG/MINOR: cache: Inverted variables in http_calc_maxage function
    - MINOR: pattern: make pat_ref_append() return the newly added element
    - MINOR: pattern: make pat_ref_add() rely on pat_ref_append()
    - MINOR: pattern: export pat_ref_push()
    - CLEANUP: pattern: use calloc() rather than malloc for structures
    - CLEANUP: pattern: fix spelling/grammatical/copy-paste in comments
diff --git a/VERSION b/VERSION
index fd42df7..0f3b5a1 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.3-dev8
+2.3-dev9