a2x Syntax Error with .asdf/PyEnv

**Describe the bug**

```

[  0%] Generating cjxl.1

  File "/home/p/.asdf/shims/a2x", line 3

    exec /home/p/.asdf/bin/asdf exec "a2x" "$@" # asdf_allow: ' asdf '

SyntaxError: invalid syntax

```

**To Reproduce**

```

which a2x

    /home/p/.asdf/shims/a2x

mkdir build

cd build

cmake ..

cmake --build .

```

**Expected behavior**

```

[  0%] Generating cjxl.1

[  0%] Generating djxl.1

[  0%] Built target manpages

```

**Environment**

 - OS: WSL2

 - Compiler version: Debian clang 17.0.6

 - CPU type: x86_64

 - cjxl/djxl version string: v0.10.2 661fec1b [AVX2,SSE4,SSE2]



**Additional context**



Line 435f of CMakeLists.txt:

```

    file(STRINGS "${ASCIIDOC}" ASCIIDOC_SHEBANG LIMIT_COUNT 1)

    if(ASCIIDOC_SHEBANG MATCHES "/sh|/bash" OR MINGW)

```

.asdf/shims/a2x

```

#!/usr/bin/env bash

exec /home/p/.asdf/bin/asdf exec "a2x" "$@" # asdf_allow: ' asdf '

```

I think the problem is the SheBang line which has "/usr/bin/env bash",

so it isn't recognized as a Shell script.

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