ci(workflows): refresh ClickHouse LTS pins (EOL 25.3 → 26.3)

ClickHouse 25.3 LTS is effectively EOL. Roll the older pinned LTS forward
to 26.3 (current second-newest LTS), and move the single-version env pins
used by non-matrix jobs from 25.3 to 25.8 — the older/more battle-tested
of the two pinned LTS, matching this repo's long-standing convention
(env vars have always tracked the older LTS; see commit 76c335d).

- build.yml: test matrix ["25.3","25.8","latest"] -> ["25.8","26.3","latest"] (x3);
  PREFERRED_LTS_VERSION "25.3" -> "25.8"
- analysis.yml: PREFERRED_LTS_VERSION "25.3" -> "25.8"
- nightly.yml:  CH_VERSION "25.3" -> "25.8"
- release.yml:  CH_VERSION "25.3" -> "25.8"

CI-only change; no client behavior change (no CHANGELOG / version bump).
Approved by @mshustov per the AGENTS.md CI-change policy.

Closes #2954

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: polyglotAI-bot

.github/workflows/analysis.yml

@@ -28,7 +28,7 @@ on:
         required: false
 
 env:
-  PREFERRED_LTS_VERSION: "25.3"
+  PREFERRED_LTS_VERSION: "25.8"
   PR_NUMBER: ${{ github.event.pull_request.number || '' }}
 
 jobs:

.github/workflows/build.yml

@@ -32,7 +32,7 @@ concurrency:
   cancel-in-progress: true
 
 env:
-  PREFERRED_LTS_VERSION: "25.3"
+  PREFERRED_LTS_VERSION: "25.8"
 
 jobs:
   compile:
@@ -151,7 +151,7 @@ jobs:
       matrix:
         # most recent LTS releases as well as latest stable builds
         # https://github.com/ClickHouse/ClickHouse/pulls?q=is%3Aopen+is%3Apr+label%3Arelease
-        clickhouse: ["25.3", "25.8", "latest"]
+        clickhouse: ["25.8", "26.3", "latest"]
         project: ["clickhouse-http-client", "client-v2"]
       fail-fast: false
     timeout-minutes: 15
@@ -303,7 +303,7 @@ jobs:
     needs: test-java-client
     strategy:
       matrix:
-        clickhouse: ["25.3", "25.8", "latest"]
+        clickhouse: ["25.8", "26.3", "latest"]
         # here http, http_client and apache_http_client represent different value of http_connection_provider
 #        protocol: ["http", "http_client", "apache_http_client"]
         protocol: ["apache_http_client"]
@@ -363,7 +363,7 @@ jobs:
     needs: test-jdbc-driver
     strategy:
       matrix:
-        clickhouse: ["25.3", "25.8", "latest"]
+        clickhouse: ["25.8", "26.3", "latest"]
         # grpc is not fully supported, and http_client and apache_http_client do not work in CI environment(due to limited threads?)
         protocol: ["http"]
         r2dbc: ["1.0.0.RELEASE", "0.9.1.RELEASE"]

.github/workflows/nightly.yml

@@ -13,7 +13,7 @@ on:
 env:
   CHC_BRANCH: "main"
   # CHC_VERSION: "0.9.0"
-  CH_VERSION: "25.3"
+  CH_VERSION: "25.8"
 
 jobs:
   nightly:

.github/workflows/release.yml

@@ -4,7 +4,7 @@ on:
   workflow_dispatch:
 
 env:
-  CH_VERSION: "25.3"
+  CH_VERSION: "25.8"
 
 jobs:
   release: