The reason is the same as for
https://github.com/varnishcache/varnish-cache/issues/2708 :

VRT_priv_task may now return NULL for out-of-workspace errors, see
https://github.com/varnishcache/varnish-cache/commit/de2b431086a13b243dc8b3e71cd8697db1df2c7f

A Host: header is now added always, which accounts for another
17 bytes for connections to 127.0.0.1

The purpose of these tests was to ensure that vmod_blobcode works identical
to shard.key(). Now that the latter has been changed to only support SHA256,
we need to remove out tests for custom hashes.

Ref: https://github.com/varnishcache/varnish-cache/pull/2558

varnish-cache commit 51176640603b123a38b49ae271cb9c9de9df1d28

Also move tests to vcl_recv for better visibility because VRT_fail
from vcl_synth just closes the connection

most of the editing has been done using the following shell commands,
but some tests were edited manually

sed -i 's:HEXLC:HEX, LOWER:g' $(git grep -l HEXLC)
sed -i 's:HEXUC:HEX, UPPER:g' $(git grep -l HEXUC)

sed -i '/VMOD blobcode must be installed/ d' $(git grep -l blobcode)
sed -i 's:blobcode:blob:g' $(git grep -l blobcode)

sed -i 's:\.decode(IDENTITY, *$:\.decode(encoded=:' $(git grep -l '\.decode(IDENTITY, *$')
sed -i 's:\.decode(IDENTITY, ":\.decode(encoded=":' $(git grep -l '\.decode(IDENTITY, "')

sed -i 's:\.decode(BASE64, ":\.decode(decoding=BASE64, encoded=":' $(git grep -l '\.decode(BASE64, "')
sed -i 's:\.decode(BASE64, *$:\.decode(decoding=BASE64, encoded=:' $(git grep -l '\.decode(BASE64, *$')

sed -i 's:\.decode(HEX, ":\.decode(decoding=HEX, encoded=":' $(git grep -l '\.decode(HEX, "')
sed -i 's:\.decode(HEX, *$:\.decode(decoding=HEX, encoded=:' $(git grep -l '\.decode(HEX, *$')

Ref: https://github.com/varnishcache/varnish-cache/issues/2297

cache.h before vrt.h

this is required for master since 81bc4cef2a5e651a9e34ae5400672a88663db7ef

This reverts commit 3b8459d7.

Return NULL and report errors in the log if a HMAC key or message
is NULL, rather than tripping assertions.

we would need to complicate testing specifically, so just mark this as
a TODO for now