GHA: Add macos-26 and remove OpenSSL 1.1 builds on macOS

The new runner doesn't have OpenSSL 1.1 available anymore
via homebrew. The formula is also marked as "deprecated"
for older macOS versions. So I think it is okay to drop
it.

Change-Id: I1633ee6207443e041434e9f0dda98afd5a22e1b4
Signed-off-by: Frank Lichtenheld <[email protected]>
Acked-by: Yuriy Darnobyt <[email protected]>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1382
Message-Id: <[email protected]>
Signed-off-by: Gert Doering <[email protected]>

Author: flichtenheld

.github/workflows/build.yaml

@@ -210,9 +210,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ssllib: [openssl@1.1, openssl@3, libressl]
+        ssllib: [openssl@3, libressl]
         build: [normal, asan]
-        os: [macos-14, macos-15]
+        os: [macos-14, macos-15, macos-26]
         include:
           - build: asan
             cflags: "-fsanitize=address,undefined -fno-sanitize-recover=all  -fno-optimize-sibling-calls -fsanitize-address-use-after-scope -fno-omit-frame-pointer -g -O1"