chore: mark Firecracker 1.8 unsupported

Firecracker v1.8 had reached EOL on 2025-01-10.

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse

docs/RELEASE_POLICY.md

@@ -92,7 +92,7 @@ v3.1 will be patched since were the last two Firecracker releases and less than
 | ------: | -----------: | -----------: | ------------------: | :------------------------------ |
 |   v1.10 |   2024-11-07 |      v1.10.1 |          2025-05-07 | Supported                       |
 |    v1.9 |   2024-09-02 |       v1.9.1 |          2025-03-02 | Supported                       |
-|    v1.8 |   2024-07-10 |       v1.8.0 |          2025-01-10 | Supported                       |
+|    v1.8 |   2024-07-10 |       v1.8.0 |          2025-01-10 | 2025-01-10 (end of 6mo support) |
 |    v1.7 |   2024-03-18 |       v1.7.0 |          2024-09-18 | 2024-09-18 (end of 6mo support) |
 |    v1.6 |   2023-12-20 |       v1.6.0 |          2024-06-20 | 2024-07-10 (v1.8 released)      |
 |    v1.5 |   2023-10-09 |       v1.5.1 |          2024-04-09 | 2024-04-09 (end of 6mo support) |